View Full Version : Wiring an alternator energizer wire question

05-17-2010, 03:24 PM
For the electrical gurus here, I have a Delco 63A alt with a batt post and #1 and #2 terms. As I understand it the #1 term. goes to the ign. sw. and gets turned on and off to energize the alt. The #2 term. goes to the batt term. and that goes to the amp meter post. Well, all that works just fine but the ign. sw. is a simple on/off and I can't segregate the coil wire from the alt energizer wire so when I shut the engine off the alt field back feeds the coil and the engine keeps running.

A simple fix is to put a diode in the wire to stop the back feed. The #1 wire draws about 2 amp and all I could get was a 3A diode. I tried a 1A before I measured the circuit and the diode got REAL hot. Well, it still gets to about 100 to 115 deg F with the 3A diode.

My question is will the 3A diode live or die or should I get a 5A or bigger diode?

05-17-2010, 03:59 PM
Unfortunately I have tossed all my old Alternator manuals, but AFAI remember, the #1 terminal is the dash warning light output, and is the initial excitation for the field there is normally a lamp in series with this connection?
#2 is the ignition switch?

05-17-2010, 04:04 PM
I think you're on the right track Carl.

I believe field current for your alternator should be 2.5-2.9 amps, so I would use the 5 amp diode.

Here's a quick basic wiring diagram for a Delco SI series alternator.


05-17-2010, 05:53 PM
MaxHeadRoom, they did have a dash light that came on when the ign was turned on but as I ripped out the rats nest of wiring they had and started over I don't know where it was wired to.

Willy, I got the same info as you showed in the drawings from the internet and assumed it to be valid. I will have Radio Shack order a 5A diode. I guess I could wire the dash light into the #1 wire but I don't see the point in having the dash light and an amp meter. They didn't even have the amp meter wired into the charge circuit anyway but I do and it shows a charge/discharge now.

This is on my 1951 CJ3A Willys Jeep and it's turning into a money pit but I kind of expected that. I am not making it into a show Jeep, just a driver mostly for getting around in the snow in the winter but I plan to drive it everyday and enjoy the hell out of it.

Thanks for the help.

05-17-2010, 06:04 PM
Carl, don't get the p/n shown in the diagram, not sure but I believe it too is a 3 amp.
The Jeep sounds like a fun project. I did one for a friend a long time ago. I miss that little Jeep. We went through that thing from one end to the other. Reliability was our main requirement, but it was a gas to drive, summer or winter. Kinda of like an all season, all road sports car.

05-17-2010, 06:07 PM
You can wire a 194 bulb in the circuit, or, just leave the field wire off, it should start charging just by goosing it, apprx 2000 RPM. I did one for a friend on a Willy's with a plow last winter. Jan

05-17-2010, 06:42 PM
IF you use an idiot lite in series with the #1 terminal you do not need a diode. The bulb acts as a bleed-off resistor, so if you use one that is too small it will light but the engine will take a few seconds to shut off.
Years ago I had a GM alternator in a race car, ran the #1 terminal through a light I had set up as a dome light inside the cockpit. Turned on the ignition while I got my belts and such on, went off automatically when I started the motor.

05-17-2010, 07:30 PM
I'm not fond of a light so I will go with the diode. I will check the RS site for the number of a 5A or more diode.