The Stovebolt Site Forums The Shop Area The Electrical Bay 1946 Chevy 1/2Ton - Alternator Wiring

I've converted to 12v with a wiring harness from Jim Carter (EL168). I'm needing some help on the correct way to wire the alternator. Instruction step #1 says to wire from the alternator to the Ammeter and then there is pigtail that goes from the Ammeter to the ignition switch for power. I have a power wire from the starter to the other side of the Ammeter. Reading the alternator instructions, it says to wire from the alternator directly to the positive post of the battery. If I do that, I just need to add a wire from the Ammeter to the ignition for power?

I'm asking because when I first tried to start my truck, my main 30A fuse would blow. I disconnected the alternator and have push on the starter many times and the fuse has not blown again. Was the fuse blowing because with the first setup the alternator was sending power through the Ammeter and through the fuse back to the start wire which then went back to the battery?

Or maybe I'm reading Step 1 wrong? I was connecting the alternator wire to the Ammeter post that had the power to the head light switch. And then there was a pigtail to the ignition.

Any thoughts or ideas are much welcomed. How are you wiring your 12v alternator?

John. I did a search on AI. Not saying it’s correct but may be helpful. Hopefully someone comes along soon with correct answers

Looks like the Jim Carter instructions are for a 1 wire alternator and you are planning to use a 3 (or 2) wire alternator.

In either case, the large wire (#10) from the stud on the back side of the alternator should connect to the stud on the ammeter where the ignition switch connects.

The other stud on the ammeter needs to connect to the battery. The easiest way to connect it is to run a #10 wire from the ammeter to where the battery cable connects to the stomp starter switch.

If you are using a 3 wire alternator ...

Connect the #1 pin on the slip on connector on the back of the alternator to a lamp (I use a 12 volt LED). The other wire on the lamp (the stripe end of the LED) connects to 12 volts that is only on when the key is on.

Connect the #2 pin on the slip on connector on the back of the alternator to somewhere in your wiring up under the dashboard that is on when the key is on. That wire tells the alternator how much voltage is actually being delivered to your wiring harness and regulates the output of the alternator to get somewhere around 14 volts to the devices in your truck.

A 1 wire alternator (and connecting the #2 pin directly to the stud on the back of the alternator) does a poor job of supplying proper voltage because it regulates to 14 volts or so at the large output stud and doesn't allow for any voltage loss in your wiring harness.

self exciting ALT. Red wire from ALT. to BATT. Ground to frame. Voltmeter thru ACC.
Ammeter won`t measure accurate for 12v. But can still be hooked up. 14.2 for charge.

Thanks guys! I got some work to figure this out.

1. I do have the "excite" wire connected to my ignition switch and it only has power when I turn on the key.

2. Power to my ignition switch comes from the starter post wire, but I'm not sure if I used a #10 wire. More likely I used a #12 and I can change that. I have a 30A fuse on this line and it was the one blowing when I'm trying to start the engine.

3. I picked up a ground wire for the alternator and I'll get that installed

4. Thanks for the AI info. That sounds pretty much what's happening in my situation.

#10 wire is good for 50 amps at 10 feet of length, 100 amps at 5 feet
#12 is 35 amps at 10 feet, 60 amps at 5 feet.

30 amp fuse is too light for the alternator output that happens immediately after starting. Needs to be closer to rated output of the alternator.


GM didn't run a separate ground wire to a 10-SI alternator.

Bill, I had no idea about connecting a lamp inline on the excite wire? Watching some YouTube and searching online sources - so I need to pick up a small light I can add. Where do others mount this light? Not wanting to drill a hole in my dash.

My '52 has Vintage Air A/C. It comes with an ABS C-channel about 2 inches tall that attaches to the bottom of the dashboard running from about the ignition switch to the right side of the cab. Vintage Air mounts their fan, mode, heat temp, A/C temp knobs and a double set of vents in the ABS roughly under the radio speaker grill.

That leaves another 18 inches or so of empty space in the ABS C-channel before the vent on the right hand end. I mounted a red 12volt LED lamp in the ABS and used it in the "exite wire" circuit. A similar blue LED is mounted next that shows if the A/C clutch is engaged. I also mounted a blue 12volt combination switch/LED nearby that controls a bed lamp and an under-bed mounted backup light.

OK - After taking a short break, I believe the re-wiring is complete. I ran the alternator wire directly to the +battery. I changed the #12 wire from the starter to Ammeter to #10 wire. I added a light inline on the excite wire from the alternator. Not the most elegant solution, but I made a little bracket to hold the light. I didn't want to drill any holes in the dash. Now I need to test.