** Resolved ** Grounding problem?

[atrout]

My wife and I went to dinner and a play the other evening. We drove the '46 Chevy, Maurice Chevrolet. Going to dinner was fine. At this point I'd like to point out that civil sunset was not until 8:46 PM. Dinner was at 6:00. Went to the theatre at 7:45....

After the play, Streetcar named Desire, Tennessee Williams.... an excellent American playwright.... I digress. Time for headlights. All on just fine, we start driving down Market Street, headlights, dash-lights, go out. I pulled over and messed with switch the wire bundle, etc. While we were contemplating what to do, I turned on the four-way flashers. Flashers all around, so this is good. Then I stepped on the brakes and the headlights and dash-lights came on, went off, came on, went off...

Needless to say we broke up laughing. I haven't run into this one before! So I'm going to replace main ground cable and put an extra bonding strap or two on. I think I'll run a jumper from battery ground straight to headlight switch and see if all symptoms go away...

Stella! Stella! I coulda been a mechanic! I coulda been a somebody!

I added the turn signals but the headlights circuitry never came into play. Any ideas?

Andy

Edited May 31, 2013 by atrout
issue resolved (see edit history)

[Guest prs519]

Another option might be to connect an ohmmeter between the various components and ground. You need also to quit poking fun at Maurice!

[Friartuck]

Was Maurice restored right about the time as the movie 2000, A Space Oddessy was released and Hal influenced Maurice... "Andy I'm afraid you can't do that now, I'll be stopping the engine soon....."

In all seriousness, there are several possible things. Assuming a stock 6 volt negative ground system:

1. The connection that supplies positive current to the headlight switch isn't getting enough power and the four way flasher circuit is robbing current before it gets to the headlight switch. The flasher circuit likley gets power before other circuits (is powered regardless of ignition switch). You mentioned you added the turn signals and may have tapped power from a convient location with an unexpected consequence.

2. Add grounding straps from the fenders (preferably near the headlights) back to a known good ground point. Add a seperate ground strap to the dash. Adding a ground to the light switch should not do anything.....switch is on the positive side.

3. Does Maurice have an amp meter in the dash?? check the connections. If you have a VOM and a fully charged battery, monitor the voltage at various locations to make sure you don't have an undersized gauge wire, especially between the generator and the ampmeter. Same goes for the wire between the ampmeter and the headligtht switch. Should be 10-12 gauge with soldered connections (terminals).

4. You mentioned you stepped on the brakes and the lights went nuts. Perhaps this was an electrical issue (again robbing power) or pressure was applied to the firewall (effecting the ground through the sheet metal).

[atrout]

I did a little troubleshooting today. More truth table stuff than actually tracking voltage drops.

I don't believe the turn signals are integral to the issue. The previous owner converted the car to 12 volt. It does not have a new wiring harness but for same power consumption the wiring should be carrying half it original 6 volt current. Certainly solid connection and good bonding needs to be addressed.

I replaced the headlight switch with one of the Chevy of the 40s OEM style 12 volt rated, rheostat, and removable shaft - $50 fairly decent manufactured switch. My dash light dimmer wasn't working on original switch.

Sitting in garage, engine off, no brake lights or flashers involved - I turn headlamps and dash lights on. After about a minute or so, I get the flashing on off behavior. It is so regular it makes me believe the new headlight switch has a built in circuit breaker in form of a bimetallic strip. I assume this would be for dash light circuitry. So aside from everything else to check, I'm going to make sure all the dash lights are 12 volts and/or eliminate the dash lights from the "issue".

Thanks for the suggestions... I hope to chase this one to ground in next day or two.

[hchris]

I did a little troubleshooting today. More truth table stuff than actually tracking voltage drops.

I don't believe the turn signals are integral to the issue. The previous owner converted the car to 12 volt. It does not have a new wiring harness but for same power consumption the wiring should be carrying half it original 6 volt current. Certainly solid connection and good bonding needs to be addressed.

I replaced the headlight switch with one of the Chevy of the 40s OEM style 12 volt rated, rheostat, and removable shaft - $50 fairly decent manufactured switch. My dash light dimmer wasn't working on original switch.

Sitting in garage, engine off, no brake lights or flashers involved - I turn headlamps and dash lights on. After about a minute or so, I get the flashing on off behavior. It is so regular it makes me believe the new headlight switch has a built in circuit breaker in form of a bimetallic strip. I assume this would be for dash light circuitry. So aside from everything else to check, I'm going to make sure all the dash lights are 12 volts and/or eliminate the dash lights from the "issue".

Thanks for the suggestions... I hope to chase this one to ground in next day or two.

Once had a similar problem and it triggered the resetable breaker in the light switch. In the end we found a wire chafing in an add on loom for trailer lights; perhaps start with an integrity check of the turn indicator wiring?

[oldford]

I don't believe the turn signals are integral to the issue. The previous owner converted the car to 12 volt. It does not have a new wiring harness but for same power consumption the wiring should be carrying half it original 6 volt current.

I think you should 'rethink' you theory. If all the previous owner did was to change the battery from 6 to 12 volts, the current is doubled not halved. V=I*R. If the loads in the car's circuits all remained the same, raising the voltage will raise the current proportionally.

Frank

[Guest prs519]

Frank, are you sure? I thought since the power was the ultimate gauge of the use of energy, then doubling the voltage for a given circuit would require only half the

current, since P=I*E.

[TexasJohn55]

Semantics (is that the right word?). Power is measured in Watts, we somtimes use the terminology of current interchangeably which is not correct, Amperage is amperage, we say that increasing the voltage will increase the current but we mean power (wattage). Is that right? Maybe I'm confused too. TexasJohn

[TexasJohn55]

Actually, I am confusing the issue so I'll hush. AND, don't want to hijack this thread.

Edited May 29, 2013 by TexasJohn55
afterthought (see edit history)

[Guest prs519]

Yes, and I will muddy the waters further by saying it is the resistance of the accessory or circuit in question which is an unchanging quantity, which controls the amount of total power that is delivered (unless it blows a fuse or burns a wire). The resistance is the only fixed (nearly) quantity. Actually, I believe you are correct (almost) in what you said, Tex. BUT for a given power draw (proportional to resistance), the product of volts and amps (power) will be the same. Tripling the voltage will require 1/3 the amps to supply the same watts. This is why in AC power the voltage is jerked way up for the purpose of transmission. There is less power loss due to an increase in voltage, as compared to an increase in current. Power is also = to the current squared times the voltage. Smaller wire size can be used by jacking up the voltage which is transformed at your home supply pole to less voltage and more current. NOW I have confused the issue, but I hope I have it right. AC or DC, in this case, same phenomenon.

[oldford]

Power is a measure of work performed. Your statement is correct if the power consumption stayed the same, but it does not... The resistance of the load did not change. The voltage increase from 6 to 12 will push twice the current through the circuit.

Frank

[Chris Bamford]

The voltage increase from 6 to 12 will push twice the current through the circuit.

Frank

I find that hard to believe. As I understand it, doubling the voltage will halve the amperage (current) if resistance is unchanged.

Six-volt battery cables need to be larger gauge to carry higher amperage than 12-volt cables.

[oldford]

V=I*R. Sorry, I did not invent the formula. Twice the voltage, twice the current, if the resistance is constant.

Frank

[oldford]

Let me try it this way, Power = voltage * current or P=V*I. Voltage is I*R, so power can be also written as P=I**R or current squared times resistance. If the resistance can be doubled by making the wires in the starter (for instance) very small and many more turns, then the same amount of power can be accomplished with half the current. Half the current allows one to get the same amount of power if the resistance is doubled. However, you need to double the voltage to make this happen. The net gain is that you can do all this with less wire and make it cheaper to manufacture. Let's see if I can show you in the formula:

Frank

[TexasJohn55]

Guys, this ain't helping the original poster however interesting. When he upgraded to 12v system, he had to change the bulbs, therefore power requirement was the same with half the amperage on the wires, TJ55

[oldford]

You could start by taking ALL of the bulbs out and replacing them one at a time and testing your switches between each bulb. I've seen two filament bulbs fail in such a way that one filament breaks and touches the other and becomes part of the new circuit. This can drive you crazy. If you find the failing bulb, throw it as far away and into the woods as you can...

Frank

[TexasJohn55]

Was Maurice restored right about the time as the movie 2000, A Space Oddessy was released and Hal influenced Maurice... "Andy I'm afraid you can't do that now, I'll be stopping the engine soon....."

In all seriousness, there are several possible things. Assuming a stock 6 volt negative ground system:

1. The connection that supplies positive current to the headlight switch isn't getting enough power and the four way flasher circuit is robbing current before it gets to the headlight switch. The flasher circuit likley gets power before other circuits (is powered regardless of ignition switch). You mentioned you added the turn signals and may have tapped power from a convient location with an unexpected consequence.

2. Add grounding straps from the fenders (preferably near the headlights) back to a known good ground point. Add a seperate ground strap to the dash. Adding a ground to the light switch should not do anything.....switch is on the positive side.

3. Does Maurice have an amp meter in the dash?? check the connections. If you have a VOM and a fully charged battery, monitor the voltage at various locations to make sure you don't have an undersized gauge wire, especially between the generator and the ampmeter. Same goes for the wire between the ampmeter and the headligtht switch. Should be 10-12 gauge with soldered connections (terminals).

4. You mentioned you stepped on the brakes and the lights went nuts. Perhaps this was an electrical issue (again robbing power) or pressure was applied to the firewall (effecting the ground through the sheet metal).

Andy, revisit this post, especially item #1 if you haven't already fixed it.

[TexasJohn55]

Andy, there should be a wiring diagram in your shop manual. If you don't have one, maybe someone could post one for you. It will take some studying but could show you where the problem is.

[atrout]

There has been some interesting discussions about Ohm's Law and the power. (Not to reopen any wounds but double the voltage to the same load results in half the amperage).

I have considered the dual filament bulb with one filament failing and shorting to the other circuit - i.e. Brake filament shorting to the tail lamp filament. This would provide a back feed into the turn signal switch making a funky parasitic circuit...

I have pulled both tail lamp bulbs and the headlights still go into disco mode after about a minute. I also pulled the case off the voltage regulator just because it acts like a relay/circuit breaker cycling . It's not the voltage regulator. I clamped a Fluke current probe over primary. Headlamps/Dash are drawing around 8.6 amps (around 103 Watts which makes sense). The meter is digital so I can't see if the current is creeping up or it is steady until "open".

Next troubleshooting session - the weather is nice here so I've been working outdoor projects - I plan to lay under the dash with a handful of jumper wires and bypass the switch contacts of the headlight switch itself.

The good news is this can be fixed - it's just one of those crazy fun old car issues!

[TerryB]

I should not get into this discussion but here goes. First, good luck with your hunt for the gremlin in your electrical system. As for the math lets look at it this way.

Assume your car when it was operating at 6 volts had a 36 watt headlamp. To get 36 watts from a 6V source you would need to draw 6 amps (6Vx6A=36w). To draw the six amps, the headlight would need to have an internal resistance of 1 ohm (6V / 1 ohm = 6A). If you connect a 1 ohm load to 12V you will draw 12A from the electrical source (12V / 1 ohm = 12A). 12V times 12A =144 watts which equals a blown fuse or burned up bulb. So in this case, the low resistance 6V bulb connected to 12V will indeed double the current draw.

For a 12V system the headlight, assuming it is also 36 watts, will need to draw 3 amps from the electrical source (12V x 3A = 36W). To limit the current to 3A requires the internal resistance of the 12V bulb to be 4 ohms (12V / 4 ohms = 3 amps). Here you can see that for an equal load in watts, only half the current is required when the source is 12V. The key is the change in bulb resistance for 12V or 6V systems. To complete the discussion, a 12v lamp with its 4 ohm resistance would draw only 1.5 amps from a 6V source ( 6V /4 ohm = 1.5A). The 12V headlight would no be too bright when connected to 6V.

Ok, that's it.

Bye

Terry

[atrout]

Issue resolved.

Turns out to be defective replacement headlight switch. Occam's Razor: The simplest solution is usually the best.

I crawled under the dash with a handful of jumper leads and started bypassing the switch contacts one circuit at a time. First headlights only... came on stayed on. Then added the taillights which also added the dash lights... still ok. Then parking lights... all on. Then I tried turn signals one at a time, then four ways. All worked with no disco effect.

I disconnected my jumpers and tried headlight switch as usual and got the flashing issue. I'm now in negotiation with the supplier of headlight switch - I bought and installed last September, but didn't drive at night until recently - to see if they will honor as a warranty replacement.

Andy

[TexasJohn55]

Bravo Andy! You had it figured right all along, why did you need us to muddy the waters? TexasJohn

[TexasJohn55]

ReQuote of post #4, I like that, especially the first statement about the "truth table stuff". TJ55

[atrout]

Thanks to all of you for your suggestions and encouragement. Keep those classics driving!

[padgett]

Seems to be a lot of confusion here but is really simple. If you take a 6v system and put a 12v battery on it & turn the lights on the watts will double and they will get very bright for a very short time.

OTOH if you replace with 12 v bulbs first, the resistance increases and the current goes in half, voltage stays the same, watts go in half and they are very dim,

Replaceing both with the same lumens 12v bulbs and a 12v battery and the voltage will double, current goes in half, and the watts stay the same brightmess is the same.

Its all about the watts & since the current is less the wires are plenty thick enough.

Of course you also need a 12v starter and this is a good time to go to a one wire alternator (no dimming at idle) and may use an adapter for a 6v radio or heater motor. If you have a cigarette lighter you want to work, use a 12v insert as it draws more power than a normal adapter can supply.

12v system can make an old car much more drivable (particularly at night) but keep all of the original parts in big baggies for the NO.

Edited May 31, 2013 by padgett (see edit history)

[oldford]

Does Ohm's Law still apply when you change the battery?

[padgett]

Yes but you need to change the circuit resistance (load) at the same time you change the voltage for the power to stay equal (EI (watts) stays the same) for the same output. Tossing in Ohm's law means that for the voltage to double and the current to half, the resistance must multiply by four. e.g. 6v/6A= 1 ohm 12v/3a= 4 ohms while 6*6=12*3. You will find that 12v devices have about four times the impedance (fancy name for resistance that includes the active part - see ELI the ICE man) of 6v devices.

For a fun study of the differences between AC and DC (why modern cars have alternators) review the war between Edison and Tesla concerning the electrification of NYC.

ps it is all simple once understood, nothing complex as in heat transfer or convergent-divergent nozzles and trans-sonic flow. Anyone who makes it sound complicated is probably trying to sell you something.

[atrout]

Follow up to issue being resolved:

I received a replacement headlight switch from Chevs of the 40's. Kudos to them for exceptional customer service. I had purchased the switch a few months before actually driving at night and discovering the problem. They replaced the switch promptly and at no expense to me! I'm a happy camper!

Andy