Wiring an alternator on vintage vehicle


Active member
Hey folks,

Hoping someone here can enlighten me on what steps I should take in wiring an Alternator into my Willys jeep. It is currently using a generator that is functioning, but I am finding that as the battery ages the system can't keep up with short town trips at night. (Running the headlights) I am suspecting that sitting at stoplights and so forth just doesn't generate enough power to keep the battery topped up and run the lights.

I'm wondering what the best route is here. Obviously I would like to find the most common alternator with a V belt drive available and install it. Should I try and find an externally regulated alternator and simply swap in the appropriate regulator? Or do you connect whatever wiring is supposed to be regulated directly and find an alternator with the regulator built in?

I understand that a 1 wire alternator is very simple to install, but not necessarily the right way to do things. There isn't any feedback to the alternator so that is just runs and doesn't increase/decrease output with load applied. Also looks like many of them need to be spun up to a certain rpm to become energized. This pretty much means that you couldn't bump start one with a dead battery, correct?

This is a 1940's/50's Willys. The wiring harness is modern from Painless wiring. Unfortunately for my learning curve my dad installed the wiring for me as a surprise. So beyond the basics I really have no clue what all is hooked up to the voltage regulator or anything. Contacted Painless wiring and all they could suggest was adding a 1 wire alternator. Just not sure that is the proper way to go!

Thanks for any advice,



I'm a big fan of generators when power demands are not high. If you don't require high-output and have just the basics: ignition, lights, heater, & wipers - there really isn't much need for anything more than the stock generator. A generator will recharge a dead battery, while alternators require battery voltage to work properly.

If you're running your battery down from short runs at night, your battery's reserve is low to non-existent and it's likely just a matter of time before it needs to be replaced. I've got two older vehicles with generators and don't have this problem, but my batteries are in good shape.

But if you're dead set on an alternator, figuring out which generator/voltage regulator wiring style you have (there are two) will lead you to which alternator conversion is simpler...


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My Series IIa Land Rover had a generator and it wouldn't provide enough power to charge the battery if the lights were on. I ended up having to hand crank the motor to get it started. I switched out the generator for a one wire GM alternator, best modification I ever made on the vehicle. As far as I know modern alternators have built in voltage regulators so the wiring should be straight forward. Mine was a little more scary as the original wiring was for a positive ground.

Happy Joe

Apprentice Geezer
IMO one of the best upgrades for automobiles (after Kettering's electric starter) is alternators; had cars with generators for many years, they were rarely more than adequate (and often not).
Have done many one wire internally regulated Delcos with out any issues in vehicles ranging from a 1942 460 fuel injected Ford pickup through M38s and CJs ranging from 3s to 7s of assorted years to rock buggies with assorted engines; carbs through fuel injection... my best advice is make/adapt good brackets and don't Mickey Mouse the wiring.
BTW, a 2 or 3 wire internally regulated alternator is almost as easy to install as a one wire.
If the Willies has a 6 volt electrical system; you will need to convert it to 12 volts including changing the bulbs, adding a coil resistor and a regulator for the gauges.
While you are in there; consider running ground wires from alternator to block, block to frame and block to body (and verify the battery to block/frame ground).

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Expedition Leader
Long-solved situation in the jeep community (and amongst tractor folks), lots of singe-wire external regulator options.

Alternator has very little to do with a bump start. It's about energizing your ignition coil and even a battery too weak to crank the vehicle should have enough juice for that. OR else it's truly dead / broken.

And I think your base premise(s) is wrong. When your vehicle is running your properly working generator should produce enough juice for all requirements. Start your vehicle and disconnect your positive cable while it runs. If it isn't working properly, your vehicle will quit running. Your battery is for cranking your starter and acting as a large capacitor for your added electrical loads.
And as for alternator output is is LOW at low RMPs, not zero. There are alternators marketed to the emergency vehicle market that are designed specifically to generate more power at idle, due to the way those vehicles are often operated.

/and once again Verkstad answers an electrical question with disdainful insult to the questioner.


Active member
It is a 12v system, and luckily it is all new so I don't have any scary connections. I really suspect the battery has just been pushed beyond its useful life, but I also feel the wakeup call of finally having a dead system in a parking lot. Got it to push start no problem, but if I was by myself I could probably forget about that security blanket.

I do regret not having a hand in wiring the jeep as now I'm sort of lost as to exactly what is doing what under the hood. My dad meant it as a surprise when I was getting burnt out on the project, but now I don't have that experience of getting it working. Oh well.

Are there better generators that are able to keep up? Maybe I could find a better generator and make no other changes?


Go with a 1 wire alternator, and be done. Simplest to do. You could do externally regulated, etc, but... why bother.

The GM 1 wire has been around a long time....it works.

You can run an alternator with a battery. Thereve been occasions in the past when the gps in my work van wouldn't turn off, and it would be dead, jumpers not long enough to reach. Swap battery, start van, and hot swap it back.

With an alternator, you can have a stone dead battery, get a jump, and the vehicle will stay running.

Yes, some of them need to have the exciter triggered...but... it's usually around 2000rpms, and that is usually alternator speed, not engine speed.



Another option is to get an alternator that is built into a generator shell so as to look stock and original. I know these are popular for vintage car owners who wish to keep their cars "concourse" or exactly as delivered from the factory.


Active member
Another option is to get an alternator that is built into a generator shell so as to look stock and original. I know these are popular for vintage car owners who wish to keep their cars "concourse" or exactly as delivered from the factory.
Powergen I think the brand is. Good idea for the future but maybe a little pricey for right now. Could always put one in later after I figure it out. It would use my original generator bracket from what I can see.

I'm going to start pointing to things under the hood and you guys tell me if I'm getting warmer or colder. Is this the battery?


Okay seriously. I've examined the wiring harness and one wire on the generator is clearly labelled "Alternator power" One wire is going to ground and the other I can't find a label on. Could I hook this right up to a 3 wire alternator? I'm still confused as to what I do with the regulator after that. Would I simply connect the output of the alternator to the output wire on the regulator? Then I also probably need a voltage gauge to replace the amperage gauge, as I'm sure an alternator would just peg the old one all the time.



Here is the wiring on it. Pretty dirt simple. Depending on your current wiring you may not need to pull anymore wires.


Rock Stacker
No thats a muffler bearing lubricator.
Are you sure?? It could be part of the piston return spring mechanism that was never installed correctly...........

I did a one wire custom build using a later delco that puts out 100amps. Literally one wire to the battery (or in my case to the isolator to split up the duties between two batts)


LR Max

Local Oaf
X2 on a one wire AC Delco 12si alternator. 95 amps seems to be "the standard", which will be more than plenty for your requirements. I would say find one that will generally fit in the same location, install a V-belt pulley, and go.

Just in case you were interested, a lot of industrial equipment use the "one wire" method, so its a perfectly solid solution.

Side note, is your vehicle positive ground or negative ground? simple way to determine this is to see which lead from the battery is bolted to the chassis. If it is negative ground, then move forward with no problems. But if it is positive ground, you need to double check your entire wiring system.


Rock Stacker
In my research on the "one wire" setup, I found two possible cons. One was if it sat on the shelf too long, it may need to be re-excited before being shipped. If it was not, the end user might end up with a "bad" alternator per se. The second is a known issue but not really a con in my estimation, the alternator has to hit a certain speed before excitation starts. In my Jeep (early SBC), it starts charging at 1100 rpm. In a three wire system charging starts when needed. No big deal for me, I start up and tap the throttle once to initiate the charging.


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