Where to pull +6V power for accessories?

[Matt Harwood]

I'm replacing the wiring harness in my '35 Lincoln and would like to add circuits for the fog lights, heater, and electric fuel pump. What's the best place to pull power for accessories? There is no regulator, only a cut-out. There is a 10-gauge wire from the generator to a primitive circuit breaker, and from there to the ammeter, to the solenoid, and to the battery. I don't like connecting directly to the battery because a discharge won't show up on the ammeter.

Is it safe to pull power from the back of the ammeter? It's fed by a 10-gauge wire that should be big enough to handle the modest draw of those light-duty accessories.

 

Where did they usually pull power when they were installing fog lights and heaters back when these cars were new?

[Bloo]

It depends...

 

Back in the day for a headlight relay like yours, they pulled from the battery or starter post. I think its a bad Idea, but that is what the instructions say.

 

Stuff inside the car was probably pulled from the ammeter, or headlight switch, which were all the same point electrically, more or less, on a lot of old cars (but I don't know how the K is wired). Fog lights probably came from there too because the switch was there, if there was no relay.

 

In my opinion, the closer to the generator the better. On a cutout system, that is the end of the cutout that connects to the car's wiring. On a regulated system, it is the "bat" terminal on the regulator. Next stop on that wire is the ammeter (and probably the light switch and/or ignition switch).

 

The further from the generator you get, the more voltage drop there will be, but sometimes it makes sense to draw from inside the dash anyway, provided the wiring is big enough for the loads in question. It would be nice if everything between the generator and the battery (and all the stops inbetween) were pretty substantial wiring. This generally means cutout/regulator >> ammeter >> battery.

 

Look at it this way. The source of current is always the highest voltage point in the system. When the generator is charging, the source is the generator, but the regulator or cutout is as close as you dare go without screwing up it's operation. If your takeoff point is there none of your light or accessory current goes through the charge wiring or any superfluous connections.

 

When the engine is off, or the cutout has cut out due to low RPM or whatever, the source is the battery and the current is flowing through the charge circuit backwards to get to your accessories. Since we expect the car to be driving and charging, the generator side is where we want to be. That could be at the cutout under the hood (usually preferable), or at the other end of that wire in the car, where it hits the light switch or ammeter or whatever it hits. That might be preferable if going to the cutout would add a bunch of extra wire length.

 

Generally you don't want to add any loads to the ignition switch in the interest of not burning it up.

 

Generally you do not want your light current going through a thermal circuit breaker for brightest lights, because they require a voltage drop to work. The other side of that coin is that a thermal circuit breaker will try to come on after a short circuit, but if you blow a fuse there is no chance of having the lights pop back on.

 

If you fuse circuits, remember that fuses are to protect the WIRE, which we don't want to catch fire on a bad day. Wherever the wire or circuit gets smaller, that's where the fuse goes to protect the smaller wire. 

 

Example: a simple fog light circuit with no relay. Ammeter/cutout >> switch >> fog lamp. The fuse goes at the ammeter end, not the fog light end. The ammeter is a high current source. If there were a short along the smaller fog lamp wiring, a fuse at the ammeter end would blow. A fuse at the light would not and the smaller wire between the ammeter and the short would get really hot and possibly catch fire.

 

 

Edited July 15, 2021 by Bloo (see edit history)

[Grimy]

Recommend studying the factory wiring diagram.  1929-forward Pierces do not have a fuse panel (unlike the earlier models, which are fuse-rich), but do have under the dash one 30A and one 10A circuit breaker.  As @Bloopoints out, this is not the greatest design.  For my supplemental electric pumps on my 1930 and 1934 Pierces, I drew power from the CB to a Bosch 12V miniaturized relay which works well on 6V *IF* the battery is close to fully charged (see below).  The relay is there to minimize amps through the unobtanium ignition switch; draw to close this relay is 0.070 amps!

 

A good friend says only *Bosch* relays, nominally 12V, will work on 6V, and that's almost always true.  Level of battery charge is the threshold as I found out in February, when I could not electric-pump prime my 1934 after a winter's nap.  The battery was at 6.12 (or so) volts, enough to spin the starter but not enough to actuate the relay to in turn actuate the pump for priming.  Fortunately, I figured it out before I took the easy way out by starter-priming.  A half-hour of charging at low amps brought the battery up and then the electric fuel pump functioned properly.

 

More modern CBs are available--and preferable, because the OEM Pierce CBs are exposed (i.e., not in a can).

[Matt Harwood]

Thanks for the feedback--I was counting on you, Bloo! Here's the wiring diagram for my Lincoln:

 

 

My headlight switch at the base of the steering column is long gone, replaced by a pull switch in the dash and a dual circuit relay on the firewall and a hi/lo beam button on the floor. I'm OK with that and have plans to hook everything up. But I found that they were powering the headlights with a wire from the battery, which isn't correct. When I installed my electric fuel pump, I pulled power from the starter solenoid--again, not ideal. I'd like to remedy all that now that I'm replacing all the wiring.

 

I bought a fuse block that I was hoping to power from the ammeter and use it for the fuel pump and fog lights and to pull power to the headlight switch to trigger the relay (the relay itself will be powered from its correct terminal on the circuit breaker).

 

I mostly wanted to make sure it was safe to pull a modest amount of power from the back of the ammeter. The fog lights take 7-8 amps and the fuel pump 4-5. The wire from the generator to the circuit breaker to the ammeter to the battery is 10 gauge, so it should be heavy enough.

 

Ultimately, is pulling power from the ammeter is OK? I suppose I could pull it directly from the cut-out on the generator or the generator terminal on the circuit breaker if that would be safer.

 

It's also kind of odd that power for the stop and back up lights is coming from the coils--ostensibly that means they only work when the ignition is on. That's really weird.

 

Thanks for your thoughts, I'm working my way through this home-made setup and trying to get it right.

[edinmass]

The amp meeter should be able to handle everything that is stock. Adding the fuel pump and extra lights are pushing it............I would wire the car as correct as possible. Install all the new harness, then figure out ho to adapt it. I understand with missing components you must make some signifigant changes. Someday you or another may get every part needed to go back to stock, and it's nice to have that option. Brillman sells wire and loom by the foot of every color and description. I stock a ton of their supplies. It is a big hit up front, but having 100 feet of multiple color and gauge wire on hand make little jobs painless. also, they sell a solid state cut out.......which is not expensive and worth having in the glove box while on tour. Look forward to photos of your fuel pump install. I always install a pressure gauge at the pump, for roadside service. I like the glass fuel filters hard plumbed in also...........Ed

[Rusty_OToole]

If you are buying a wiring harness ask the seller. They should be able to add what you need.

 

I would look to take power from the terminal block. In the case of a heavy current draw like fog lights would take power off the battery circuit, controlled by a relay.

[Bloo]

Yes, you can pull from the ammeter (preferably generator side). On many cars it is just the other end of the wire coming from the generator cutout. On that Lincoln diagram, it goes to the breaker first, and then on to the ammeter from the same terminal. If that terminal is a nice stout terminal with a screw you could put a ring on, I might use is because it is a little bit closer to the generator. That terminal, or the ammeter, (or the cutout), is the preferred place to pull current.

 

No matter what you do, all the extra current will be coming through the ammeter part of the time. If you connect to the generator side, when the engine is running and the system is charging, the current is diverted away before it gets to the ammeter. But, with the car off the current IS running through the ammeter, backwards.

 

The only time I would consider connecting to the battery side is for some accessory that will mainly be used with the engine off. Even then it's bad because any current it uses registers as "charge" with the engine running.

 

The only way the ammeter would be endangered by connecting loads to the generator side as I suggest, is if all the loads you connected there, plus what Lincoln already had connected there exceed the full scale reading of the ammeter. Then, if you turned it all on with the engine off, or you were driving with it all on and stalled, the ammeter would peg "discharge" and possibly burn up.

 

In that case you would need to experimentally add a shunt to the ammeter to make it's full scale reading higher than it was originally. A bigger problem is that the charging system wont keep up when driving no matter where you connect the lights. This is kind of an edge case, but does need to be considered if you have aftermarket lights because many 1930s charging systems are too small to carry extra lights. 

 

 

Edited July 15, 2021 by Bloo (see edit history)

[Matt Harwood]

I think I will pull power for the fuel pump and fog lights from that terminal on the circuit breaker rather than the ammeter. There's also a terminal on the circuit breaker for the horns and given how seldom they are used, maybe that's a better choice? I don't know if that terminal is set up for constant duty but I'd assume it's no different than the other two. I was going to put the horns on a relay anyway.

 

I don't think I can have enough accessories running with the engine off to peg the ammeter in the negative direction. It would only be headlights, fog lights, and fuel pump at most, and maybe leaning on the horn. Not sure when all that would happen at once, but it's still less than 30 amps.

 

Thank you for the information, it was very reassuring that I wasn't going to burn the car down!

[Bloo]

It's got a 30 amp ammeter? Wow. Well, that helps.

 

10 minutes ago, Matt Harwood said:

There's also a terminal on the circuit breaker for the horns and given how seldom they are used, maybe that's a better choice? I don't know if that terminal is set up for constant duty but I'd assume it's no different than the other two. I was going to put the horns on a relay anyway.

 

As long as it is a screw on the same piece of metal, in other words NOT actually going through the circuit breaker it should be fine.

 

 

 

 

Edited July 15, 2021 by Bloo (see edit history)

[Bloo]

11 minutes ago, Matt Harwood said:

I don't think I can have enough accessories running with the engine off to peg the ammeter in the negative direction. It would only be headlights, fog lights, and fuel pump at most, and maybe leaning on the horn. Not sure when all that would happen at once, but it's still less than 30 amps.

 

Maybe splitting hairs at this point, but that also includes anything Lincoln had already connected on the generator side, like all the stuff on the circuit breaker and the ignition switch. I edited my post because it was unclear about that.