How to Sort and Maintain a Prewar car

[Steve_Mack_CT]

I know a guy who needs one of those... 

[Matt Harwood]

Let's talk about more sorting stuff. Sitting in my living room watching a rerun of "Magnum PI" which is perhaps the greatest show ever made. But I digress.

 

One of the other things I always do when I get a new-to-me old car is tune up the starting system. I have yet to acquire an old car of any kind that started easily when it came off the trailer. Melanie's 1956 Chrysler? Dead battery because the cut-out in the regulator was bad and the battery was trying to turn the generator as an electric motor. '41 Buick Limited? Battery so weak it barely turned over and I had to pop the clutch backing off the trailer to get it to fire the first time I ever drove it. The Car Which Shall Not Be Named? Impossible to start when hot--like the battery was almost dead. '29 Cadillac? Same thing. Felt like no juice to turn the starter--not even a little.

 

The first thing a lot of guys do when faced with a hard start situation is install a new battery. And they're often surprised when it doesn't help. If they have a jump box, they'll throw that on there and sometimes it forces the car to start because of the additional amperage. After that, many car guys simply assume that 6V systems just don't have what it takes and that they were always a problem, and that's why automakers switched to 12 volts. Not true, but how many of you have purchased old cars with 8V batteries already installed?

 

The reality is that all old cars with 6V electrical systems started easily, hot or cold, regardless of the weather. They didn't struggle, they didn't need a boost, and they cranked easily. But the electrical system, like the fuel and cooling systems, needs to be clean and clear to do its job, and age takes a toll even on electrical connections.

 

The first thing I do with my personal cars when they arrive is to charge the battery fully. That way I can diagnose the other parts in the system. With a healthy battery, you can see if generator output is adequate and you'll know whether the starter is healthy when it cranks. 

Step two is to examine and possibly replace the battery cables. If your car is like most, the cables are either ancient or wrong. They are quite likely a big part of the problem. 

 

Typical battery cable in an old car. It's trash.

 

If you have any concerns at all about the condition of the battery cables, replace them. If you have a 6V car and the cables are smaller than your thumb, replace them. In the grand scheme of things, they're not expensive and they're cheap insurance. As we've discussed here many times before, it is not uncommon for people to install 12V battery cables on a 6V car simply because that's what is available at the local Autozone. They don't understand how electricity works. According to Ohm's Law, lower voltage needs more amperage to do a given amount of work, and more amperage needs bigger cables because current travels along the outer surface of a wire. Less surface area = more resistance and less current moving (it's also why stranded cables are better than solid). Resistance is why undersized wires get hot. It's like a hose trying to pass a given amount of water--the smaller the hose, the higher the pressure. Eventually the hose will burst. 

 

Anyway, you can get nice, big 0 or 00 gauge battery cables at many automotive electrical shops and there are mail-order places like Rhode Island Wiring that will make you custom battery cables any length you want. I'm lucky that I have Certified Auto Electric a few miles away (Jeff, the owner, posts here occasionally) and they make beautiful silicone-covered cables that are not only plenty large but also incredibly flexible. So that's step two: upgrade your battery cables (but don't go buying them yet, there's another step first).

 

Heavy-gauge battery cables are a MUST. Check out the
awesome flexibility on these made by Certified Auto Electric.

 

In many cases, a strong battery and big cables will be enough to start your car. Plenty of current is flowing, the battery is healthy, and the starter should turn under most circumstances. But heat is still the enemy--as temperature goes up, so does electrical resistance, both in the cables and in the starter itself. Heat is the starter's enemy. You know what generates a lot of heat in an electric motor? Resistance. You've got a big hit of current flowing TO the starter, complements of your new battery cables, but to do actual work, electricity has to move from power to ground. Resistance inhibits current moving through a device and you lose energy as heat instead of doing work (i.e. turning the starter). To use the hose analogy again, if you're using a 1-inch hose on the input side, but your output side is only a 1/2-inch hose, that bottleneck is going to waste a lot of energy doing nothing but fighting its way out.

 

While you're installing your new battery cables, it should go without saying that you should clean every cable contact point to bare metal. Use dielectric grease to seal the union. Don't paint it.

 

  

All your ground points should be bright, clean metal before installing your new cables.

 

Step three is to improve your grounds to give the power an easier path to follow to and from the device it's powering. Most starters are grounded through their housings, which are bolted to an engine block or transmission bellhousing, which is bolted to the chassis somehow. When it was new and all the metal was clean and fresh, there was probably an adequate ground path. Decades later? Meh. Grease, rust, paint, and dirt have surely accumulated on the various parts, which interferes with the flow of current. Many frames are riveted and that means separate parts that are only connected to one another by the surface area of those rivets, which doesn't provide much of a path for big current. To improve the ground, clean all the various contact points for the starter. If you feel ambitious, remove the starter and really clean all the mounting points and flanges. No paint, no grease, just bright, shiny metal. When you reinstall it, use a little dielectric grease to keep the contact points clean.

 

Still, if your engine is the ground path and it's sitting in rubber engine mounts in a painted frame, it may not be enough. I always add a second and maybe even a third ground strap. You can't have too many grounds, so connect everything to everything else. The most important one is from the battery's ground to the starter housing--this gives the starter a clear ground path back to earth. Since this cable is assisting the starter housing's ground, it doesn't really need to be 00 gauge (although there's no such thing as a wire that's too big). This is one place where the 12V parts store cables are OK to use. They come in various lengths and with different terminals, including bolt-on loops at both ends, which is useful. Clean the mounting bolt or stud, as well as the starter housing around it, and attach your ground cable here and to the battery's ground.

 

  

Give your starter's ground path an assist in the form of an additional ground cable

directly to the battery's ground.

 

While you're at it, add a ground strap from the engine block or head to the frame, and from the body to the frame, getting them all as close to the battery ground as possible. Clean all your mounting points to bright metal and seal with dielectric grease. Add all the grounds you want, they can't hurt and may actually help cure other problems in the car such as wonky gauges or a radio that doesn't tune very clearly. 

 

Perhaps you want to add a cut-off switch as well. Good idea. If you use one of those green knobs on the battery terminal, go ahead and throw your tools in the lake and take up gardening or something. That's a terrible idea. Get a heavy-duty cut-off switch designed for just this purpose, and make sure it's rated for the substantial current levels of a 6V system. The are some switches rated at 50 amps and some rated at 300 amps continuous current (as much as 2000 amps intermittent). Guess which one you want? They look the same, but they're not. Buy the big, expensive one. It's common practice to put the cut-off switch on the ground side, which is what you should do. From the battery to the switch to the clean ground point on the frame or engine. More dielectric grease as needed, and tight connections. Put the switch somewhere that is easy to reach--you don't want to have to remove the front seat every time you need to turn off the battery.

 

  

Cheap parts store 50-amp disconnect switch connected by crumbling and/or undersized cables.

More fail workmanship by someone who didn't understand what they were doing. No wonder

the cursed thing never worked right.

 

This is the one you want. It'll handle 300 amps continuously and 

2000 amps for 30 seconds. Costs almost $50. Worth it.

 

  

Crap and crap. Do not use.

 

With all this new equipment in place with bright, shiny, clean grounds, your car will crank. If you still have trouble, say, with a big cubic inch brass engine or a high-compression V8, then maybe you upgrade your battery. My '29 Cadillac starts fine on a single 6V, 800 CCA Optima. My '41 Buick is perfectly happy with an original-style long, thin Group 3EH which has something like 550 CCA. The Car Which Shall Not Be Named had 414 cubic inches of V12 to crank, so I went with dual Optimas in parallel, which kicks out 1600 cold cranking amps--there was just no way for that f*cker to NOT start, regardless of how hot it got. Oh, you want to see how to hook up two Optimas in parallel? OK, here you go:

 

 
Two 6V Optimas in parallel kick out 1600 amps and have enough reserve
power that you could probably drive your car home using the starter alone.

 

If you're still having starter problems after this, you're going to have to dig deeper. First stop is the starter motor itself--worn starter bushings are common and can lead to hard starts. If that's not it, you have bigger problems to solve and you're not just sorting anymore. But that's not really part of this discussion. 

 

Again, the bottom line is to do the entire system front to back and spend the money to get the right components to make it work its best. 

 

 

 

 

Edited December 6, 2019 by Matt Harwood (see edit history)

[Bloo]

^^ This. This right here.

[zepher]

Electrical cables and connections have been a well discussed topic on the PAS forums.

Matt is right, there are far too many cars out there with inferior cables and marginal batteries.

 

[wayne sheldon]

3 hours ago, Matt Harwood said:

 

  

Crap and crap. Do not use.

 

 

Point of fact, I am NOT technically an electrical engineer. However, my dad was. And I worked with my dad for much of my adult life.  And I was a contractor in electrical and communications systems most of my working life. I was a respected fault finder in most things electrical for many years. That means I was the guy people called in to find a problem after several other people spent a couple days, and could not find it! I would go in, ask a few questions. run a few tests with my various pieces of equipment. Make a few calculations, point and say "Dig here!" (Or cut into the wall, or whatever obstacle hid the failure.)

We also occasionally consulted with fire marshals after building fires to help find the cause if it was electrical in origin. 

 

Let me add to what Matt H said about those. They are BEYOND CRAP and WORSE CRAP and can actually CAUSE FIRES on their own!!!!!

 

Thank you Matt H for pointing those out here.

[hidden_hunter]

The one I bought was specifically for vintage cars (and referenced 6v cars) and it was considerably more solid that any of the others. All of the electrical connection is encased and you push in to enable and pull out to disable - very simple and quick to do if you needed to do it in a hurry

 

was about $50 and made in Australia 

[deaddds]

Got a name for the supplier?

[alsancle]

Matt,  great, great, great point about the battery, cutout and cables.    People pay no attention to the gauge of  6 volt cables and it is such a big deal, especially if they are longer.

 

Here is the setup in my Royale.

 

[John_Mereness]

1 hour ago, alsancle said:

Matt,  great, great, great point about the battery, cutout and cables.    People pay no attention to the gauge of  6 volt cables and it is such a big deal, especially if they are longer.

 

Here is the setup in my Royale.

 

Nice !

[John_Mereness]

I just had Rhode Island Wire make me 00 cables for the 1936 Auburn 852.  

 

Someone said to me the other day - well the original 0 wcables worked just fine - well, yes they did "just what they were supposed to (Auburn probably bid it out and took the lowest bid or ....) - I am dealing with car near 85  years old car, paint all over every part, like nice bright lights, like starting when hot on a fresh/tight engine rebuild, and ...

[Graham Man]

Moroso 74102 Battery/Alternator Disconnect Switch - 300 Amp - 2000 Amps Surge

 

Battery Disconnect Switch, Super-Duty

Moroso's Super-Duty switch with rating of 2000 amps intermittent and 300 amps continuous is perfect for engines with large starter draw, RVs, Drag Cars with alternators and other applications (20 amps on small terminals)

Two pairs of copper studs (1/2" -20 & 10 -32) make it ideal for disconnecting alternator (or other electrical device) in addition to the battery

Sealed shaft keeps out moisture and debris

Indexing pin aligns switch with mounting panel and prevents rotation; fits mounting panels up to 1/4" thick

Includes switch position face plate; also includes decal to indicate switch location during emergencies

Use with Moroso Push/Pull Kit No 74105 for remote installations and Moroso Battery Cable Fitting End Kit with 1/2" opening No 74172

Part #    AVAILABLE OPTIONS

74110    Boots for Battery Disconnect Switches

74105    Push/Pull Battery Disconnect Mounting

74107    Alternator Shutdown Relay Kit

74172    Battery Cable Remote Fitting End Kit

 

 

Just type in the part number, available at all part stores

[John_Mereness]

1 hour ago, Graham Man said:

Moroso 74102 Battery/Alternator Disconnect Switch - 300 Amp - 2000 Amps Surge

 

Battery Disconnect Switch, Super-Duty

Moroso's Super-Duty switch with rating of 2000 amps intermittent and 300 amps continuous is perfect for engines with large starter draw, RVs, Drag Cars with alternators and other applications (20 amps on small terminals)

Two pairs of copper studs (1/2" -20 & 10 -32) make it ideal for disconnecting alternator (or other electrical device) in addition to the battery

Sealed shaft keeps out moisture and debris

Indexing pin aligns switch with mounting panel and prevents rotation; fits mounting panels up to 1/4" thick

Includes switch position face plate; also includes decal to indicate switch location during emergencies

Use with Moroso Push/Pull Kit No 74105 for remote installations and Moroso Battery Cable Fitting End Kit with 1/2" opening No 74172

Part #    AVAILABLE OPTIONS

74110    Boots for Battery Disconnect Switches

74105    Push/Pull Battery Disconnect Mounting

74107    Alternator Shutdown Relay Kit

74172    Battery Cable Remote Fitting End Kit

 

 

Just type in the part number, available at all part stores

This is more or less what I have been using - better situated to move some power through the car - that said, also a little hard on the hands to turn it on/off. 

[zepher]

10 hours ago, hidden_hunter said:

The one I bought was specifically for vintage cars (and referenced 6v cars) and it was considerably more solid that any of the others. All of the electrical connection is encased and you push in to enable and pull out to disable - very simple and quick to do if you needed to do it in a hurry

 

was about $50 and made in Australia 

Since the details about the twist one were posted, can you post the details about the push/pull one?

 

Thanks!

[hidden_hunter]

I'll see if I can find a brand marking on it, I checked the website of the place I bought it from and they don't seem to have it listed (they only have their core products) 

[hidden_hunter]

It's an ANBI switch 

 

https://www.anbiswitch.com.au/how-it-works

https://www.anbiswitch.com.au/cars

 

I replaced the nuts with imperial size so I didnt' have a bunch of metric on my car 

 

I also like the fact it's really easy to see if it's on or off, some of the designs are quite hard to see at a glance if it's connected.

 

It works well in combination with the fuel cut off that I have on my car (it's independently switched as well) but it gives that extra piece of mind.  

[m-mman]

On 12/5/2019 at 8:14 PM, Matt Harwood said:

If you have any concerns at all about the condition of the battery cables, replace them. They don't understand how electricity works. According to Ohm's Law, lower voltage needs more amperage to do a given amount of work, and more amperage needs bigger cables because current travels along the outer surface of a wire. Less surface area = more resistance and less current moving. It's also why stranded cables are better than solid.  Although there's no such thing as a wire that's too big. . . .

 

 

Ok, its not prewar, BUT it is a ampere hog.

My 1971 Cadillac ambulance. Lights, siren, 3 different HVAC blowers, etc. All expected to operate with long idle periods at a emergency scene. equipped with a 140+ amp alternator that also puts out A/C (for an incubator) it has two batteries from the factory. 

It came with standard 12v type cables. A friend who has industrial sized tools assembled for me 0000 cables!  Yeah almost an inch of stranded copper. No they dont flex as tight as yours do (it was a problem installing them) but guaranteed no issues from being undersized 

 

On 12/5/2019 at 8:14 PM, Matt Harwood said:

While you're at it, add a ground strap from the engine block or head to the frame, and from the body to the frame, getting them all as close to the battery ground as possible.

 

1960-61 Corvair issued a service bulletin. Reports of broken clutch cables.

Turned out accessory ground cables were not being installed/used and the return starter current was going through the clutch cable heating it and causing them to snap. Grounds are good. 

 

Edited December 7, 2019 by m-mman (see edit history)

[Bloo]

1971 Cadillac? You can bet it had something bigger than the standard parts store stuff when Cadillac built it. I had a 69 (high compression 472) that REALLY had issues cranking with the cheapie cables the former owner put on. After having that and several other issues fixed, it still drew a lot of current cranking, 350 Amps IIRC. It cranked nice and fast with the 00 cables I had made for it.

[zepher]

@hidden_hunter how sturdy is the overall switch?

In the video it looked very easy to use but also looked a little wobbly.

If it is sturdy enough I may go with this one.

 

 

[hidden_hunter]

22 minutes ago, zepher said:

@hidden_hunter how sturdy is the overall switch?

In the video it looked very easy to use but also looked a little wobbly.

If it is sturdy enough I may go with this one.

 

 

Seems sturdy enough, it has double sided tape to fix the main housing to the battery 

[edinmass]

4 hours ago, m-mman said:

 

 

Ok, its not prewar, BUT it is a ampere hog.

My 1971 Cadillac ambulance. Lights, siren, 3 different HVAC blowers, etc. All expected to operate with long idle periods at a emergency scene. equipped with a 140+ amp alternator that also puts out A/C (for an incubator) it has two batteries from the factory. 

It came with standard 12v type cables. A friend who has industrial sized tools assembled for me 0000 cables!  Yeah almost an inch of stranded copper. No they dont flex as tight as yours do (it was a problem installing them) but guaranteed no issues from being undersized 

 

 

1960-61 Corvair issued a service bulletin. Reports of broken clutch cables.

Turned out accessory ground cables were not being installed/used and the return starter current was going through the clutch cable heating it and causing them to snap. Grounds are good. 

 

 

Grounds are good........once saw a pre war Cadillac that was using the fuel line as the ground for the engine......always wondered if it would melt under enough load. I didn’t hang around to find out about the repair.

 

 

 

[ericmac]

I have been dealing with a starting issue with my '62 Lincoln for quite a while now, especially when the car is hot. As I look at Matt's very useful post I think I know the first place I need to start.

At this point I must plead guilty as charged. I confess to my use of a junk shut off switch, purchased from Auto Zone. I further plead guilty to the second count, my failure to use dialectic grease in the installation of that junk shut off.  And to my lack of a ground cable at the starter which was installed without sanding and subsequent use of dialectic grease. And I think those might be 0 gauge cables...but probably with a car like this I need 00 at least.

This is among the very best threads I have ever read here guys. Thanks to all of you who are sharing this knowledge. It feels like I have enrolled in a graduate course in automotive sorting. Taking this course is forcing me to study my car. Hard. That's a good thing. 

Edited December 7, 2019 by ericmac
Correction (see edit history)

[ted sweet]

15 hours ago, hidden_hunter said:

It's an ANBI switch 

 

https://www.anbiswitch.com.au/how-it-works

https://www.anbiswitch.com.au/cars

 

I replaced the nuts with imperial size so I didnt' have a bunch of metric on my car 

 

I also like the fact it's really easy to see if it's on or off, some of the designs are quite hard to see at a glance if it's connected.

 

It works well in combination with the fuel cut off that I have on my car (it's independently switched as well) but it gives that extra piece of mind.  

any way to buy them if live in usa?

[ted sweet]

On 12/6/2019 at 2:53 AM, wayne sheldon said:

 

 

Point of fact, I am NOT technically an electrical engineer. However, my dad was. And I worked with my dad for much of my adult life.  And I was a contractor in electrical and communications systems most of my working life. I was a respected fault finder in most things electrical for many years. That means I was the guy people called in to find a problem after several other people spent a couple days, and could not find it! I would go in, ask a few questions. run a few tests with my various pieces of equipment. Make a few calculations, point and say "Dig here!" (Or cut into the wall, or whatever obstacle hid the failure.)

We also occasionally consulted with fire marshals after building fires to help find the cause if it was electrical in origin. 

 

Let me add to what Matt H said about those. They are BEYOND CRAP and WORSE CRAP and can actually CAUSE FIRES on their own!!!!!

 

Thank you Matt H for pointing those out here.

been using the screw type for over 30 years with no issues

[edinmass]

3 hours ago, ericmac said:

I have been dealing with a starting issue with my '62 Lincoln for quite a while now, especially when the car is hot. As I look at Matt's very useful post I think I know the first place I need to start.

At this point I must plead guilty as charged. I confess to my use of a junk shut off switch, purchased from Auto Zone. I further plead guilty to the second count, my failure to use dialectic grease in the installation of that junk shut off.  And to my lack of a ground cable at the starter which was installed without sanding and subsequent use of dialectic grease. And I think those might be 0 gauge cables...but probably with a car like this I need 00 at least.

This is among the very best threads I have ever read here guys. Thanks to all of you who are sharing this knowledge. It feels like I have enrolled in a graduate course in automotive sorting. Taking this course is forcing me to study my car. Hard. That's a good thing. 

 

 

Your radiator hose hose is bad......they rot from the inside out. Take it off and cut it open and flex it........

[billorn]

2 hours ago, ted sweet said:

been using the screw type for over 30 years with no issues

 

Because of that if you ever have a problem you wont look at the knob cutoff as the problem and will have a hard time diagnosing a problem and solving it. They work on some cars and dont work on other cars. Definitely a no go on 6 volt cars tho. That screw is what is passing current and only where its touching the other thin parts. You can have cables as big as you're wrist but all the power is still trying to go thru a connection smaller then a pencil. It works despite the knob cutoff not because of it.

[zepher]

2 hours ago, edinmass said:

 

 

Your radiator hose hose is bad......they rot from the inside out. Take it off and cut it open and flex it........

 

You can tell that hose is bad because of how swollen it is.

Good eye, Ed.

[zepher]

3 hours ago, ted sweet said:

any way to buy them if live in usa?

 

They are on Flea Bay but shipping is a killer.

 

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=anbi+switch&_sacat=0

[ted sweet]

7 minutes ago, zepher said:

 

They are on Flea Bay but shipping is a killer.

 

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=anbi+switch&_sacat=0

not paying 90 bucks for one

[zepher]

1 minute ago, ted sweet said:

not paying 90 bucks for one

 

I agree.

 

Maybe we can get one of the Aussie members to buy them and ship them to the US for us?

It's bound to be cheaper.

[hidden_hunter]

57 minutes ago, zepher said:

 

I agree.

 

Maybe we can get one of the Aussie members to buy them and ship them to the US for us?

It's bound to be cheaper.

 

 

Does Amazon ship it over there?

https://www.amazon.com.au/Altronics-ANBI-Switch-Battery-Isolator/dp/B07L8KZDFD/ref=sr_1_1?keywords=anbi+switch&qid=1575755705&sr=8-1

 

I would also suggest messaging some of the ebay sellers, ebay's postage calculators are normally pretty exorbitant. The same happens for us when we use US ebay, and normally if you contact the seller you can get something a lot more reasonable 

 

You could also try messaging them https://www.anbiswitch.com.au/enquiries to see if there is a US distributor

 

The Australian $ is pretty much back to being the pacific peso at the moment, AUD$50 = US$35 so when you're looking at prices factor that in. Shipping in Australia is typically pretty expensive, you'd be looking at about US$15 to ship that switch to the US if you use Australia Post (which most people would). 

 

The other option is to use a package forwarding place, which are reasonably common to use here but I suspect not so much in the US. Typically you pay a small handling fee (normally about $5) + the actual postage cost. 

 

If you don't have much luck, I could probably do it in a pinch - I just couldn't guarantee when I could get to the post office to send it as I'm away for work for a bit in the next couple of weeks 

[alsancle]

4 hours ago, ted sweet said:

been using the screw type for over 30 years with no issues

 

 

I had one fail and one cook.   After the cooked one I learned my lesson.

[ericmac]

6 hours ago, edinmass said:

 

 

Your radiator hose hose is bad......they rot from the inside out. Take it off and cut it open and flex it........

Thanks for that Ed. Just as a guess, I am betting you would recommend changing all the hoses because if one is bad, they are probably all bad. So I'll take that preemptive advice and change them all.

Edited December 8, 2019 by ericmac (see edit history)

[wayne sheldon]

"been using the screw type for over 30 years with no issues"

 

Like alsancle, years ago, I too had one of those cook. On a car I had just bought, and had had only a few days. I already knew I didn't like the idea, even though I hadn't seen one up close. I was checking the car over and fiddled with it just a little. A couple minutes later, while looking at something else, I began to smell something. I quickly realized it was the battery cable, and the "disconnect" was smoking! This was years ago, and I didn't yet have my newfangled temperature reader (I use to diagnose overheating issues among other things). But I would estimate the "disconnect" was somewhat over 400 degrees Fahrenheit. Fortunately, I caught it quickly,and no real damage was done.

Bad designs are bad designs. Just because it hasn't failed a thousand times, doesn't mean it won't fail tomorrow.

[Matt Harwood]

On 12/7/2019 at 12:41 PM, ted sweet said:

been using the screw type for over 30 years with no issues

 

I note all your cars are 12 volt. 12-volt systems are far more tolerant since the higher voltage requires less amperage to do the same work. As a result, smaller cables and bottlenecks like a cut-off switch don't have as big an impact on function (in fact, the ability to use smaller wires was a factor in the industry's move to 12-volts because they could save money and weight). My guess would be that your cars are working despite the cut-offs not with them. I doubt removing/changing them would improve anything but if you do start to have starting or charging problems, pull those off before you do anything else. We remove the knob- and blade-type cut-offs when cars show up in our shop wearing them, just to avoid any problems later. I've never had one go up in smoke, but I have had cars that act like they have very soft batteries and removing these cut-off switches often cures the issue. On 6-volt cars, of course, these are a VERY bad idea--they can't possibly pass enough current to even crank a Model A adequately. For 12V cars it's often a crapshoot--some cars OK, some cars (as others are showing above) they are probably a source of issues. 

 

The real bottom line is that anything you can do to remove resistance from your electrical system is a good idea. Low-grade cut-off switches are an easy first step. 

Edited December 8, 2019 by Matt Harwood (see edit history)

[zepher]

48 minutes ago, Matt Harwood said:

12-volt systems are far more tolerant since the higher voltage requires less amperage to do the same work.

 

I have heard that modern cars will be moving to 48v systems for this very reason.

Modern cars have massive electrical needs and all that wire adds a significant amount of weight, as you mentioned.

 

https://autoweek.com/article/technology/48-volt-systems-are-bringing-more-power-and-better-fuel-economy

 

https://www.bmwblog.com/2018/11/16/bmw-to-debut-48-volt-electrical-systems-by-2020/

 

Sorry for the slightly off-topic post but I thought it reinforced your point, Matt.

 

[Bloo]

I have been looking for a suitable switch for my 36 Pontiac for a while now.

 

To be perfectly clear, I don't believe in disconnect switches at all, as I have seen so much trouble. Every connection matters, and so does every piece of wire between the battery and the starter. To make a car crank with authority, you remove as many connections as possible, and improve the ones you can't get rid of.

 

Here is a typical situation with a lever switch, you are adding: 1) a crimp connection from the connector where your new cable bolts to the frame, to the cable itself (solder would be better), 2) a crimp connection from the wire back to another connector at the switch (solder would be better here too), 3) a pressure connection from the connector to the nuts on the switch, 4) a connection from the nuts, through the threads, to the copper bolt that forms the switch contact, 5) a connection from the copper bolt to the copper disc that does the switching, 6) a connection from the disc to the other copper bolt 7) a connection from the copper bolt to the nuts and finally 8.) a connection from those nuts back to the battery cable that was originally bolted to the frame. Adding all that causes voltage drop, maybe a little or maybe a lot, and generally gets worse over time.

 

Nevertheless, my Pontiac has it's original wiring harness, and though it is in fairly good shape, I would prefer to shut things off when I am not using the car. An ounce of prevention, etc.. I looked into those "green knob" switches because they appear to add less connections than some of the other options, and being made of brass, there would be no dissimilar metal connection between it and my negative cable terminal. The thing was, I didn't quite have room for it. I bought a couple of versions and set about modifying them to fit in the available space. I broke the first one. Guess what I found out?

 

You really have to take one apart to see what the issues are. First of all, there is an area where the current is not flowing through much metal at all, that is where it broke. Secondly, it is not made of brass, it is a cheap zinc casting dyed gold. I looked around thinking I could find a better quality version. Nope. There are several versions but the suppliers all say "color: brass" or some such nonsense to cover up the fact it isn't, or they don't say at all. I contacted a bunch of sources, and I do not believe a brass version, or any sort of a high quality version of this part exists. Prove me wrong, and I'll buy one.

 

Still looking for the best option for a switch..... I would be game to try the Australian one if it weren't so expensive to ship. It looks like it would actually fit under my battery cover.

 

Edited December 8, 2019 by Bloo (see edit history)

[hidden_hunter]

On 12/9/2019 at 4:03 AM, Bloo said:

Still looking for the best option for a switch..... I would be game to try the Australian one if it weren't so expensive to ship. It looks like it would actually fit under my battery cover.

 

has anyone contacted them to see if they have a US distributor? 

[Matt Harwood]

On 12/6/2019 at 9:38 PM, hidden_hunter said:

It's an ANBI switch 

 

https://www.anbiswitch.com.au/how-it-works

https://www.anbiswitch.com.au/cars

 

I replaced the nuts with imperial size so I didnt' have a bunch of metric on my car 

 

I also like the fact it's really easy to see if it's on or off, some of the designs are quite hard to see at a glance if it's connected.

 

It works well in combination with the fuel cut off that I have on my car (it's independently switched as well) but it gives that extra piece of mind.  

 

Looking at their "how it works" page suggests this switch is little better than a blade-type cut-off switch. The contact area between the two parts of the switch is pretty small and it appears to be nothing more than a flat piece of metal inside that housing. It might be safer than a blade-type switch and it's surely OK for 12-volt systems, but I would not use this switch on a 6-volt car. Remember that current travels along the outer surface of a conductor, which is why big, stranded cables are by far the best. It's all about surface area. The flat pieces of metal in this switch and the minimal contact area will likely be a bottleneck on a 6V system.

 

Have a look:

 

 

That little contact patch will probably not be sufficient to pass 1000 amps of current @ 6V to crank a big cubic inch engine. Model A? Sure. Packard straight 8? Unlikely. Bigger is ALWAYS better when it comes to electrical systems on old cars.

[Dave39MD]

This one may be over kill but I am going to try it .At 300A continuous , 2000A intermittent it should handle 6 v. It is heavy, feels close to a pound.

 

Cole-Hersee 75908-BX

 

Dave

[Matt Harwood]

9 minutes ago, Dave39MD said:

This one may be over kill but I am going to try it .At 300A continuous , 2000A intermittent it should handle 6 v. It is heavy, feels close to a pound.

 

Cole-Hersee 75908-BX

 

Dave

 

That's the right one. I have it on all three of my 6V cars.