3 wire gm alternator

ldj · Apr 7, 2022

I read in wiring one up to either use a charge light or a diode. Am I reading right? I don't understand, a diode lets current pass only one way and a light bulb will let current pass either way. Why will a light bulb work and if it will why have anything there?

old · Apr 7, 2022

Either one work because it either stops current from flowing ack to the ignition circuit or in the case of a light bulb it has enough resistance to stop the back flow of current that causes feed back to the ignition system. A ballast resister will also work

caterpillar guy · Apr 8, 2022

A simple toggle switch will work also. Just can't forget to shut it off.

Dieseltech · Apr 8, 2022

Another way is to hook the excite wire into the headlights wire, then turn lights on/off to excite the system. The excite terminal does not need to stay energized all the
time.

grandpa Love · Apr 8, 2022

Diode is simple, I buy em at radio
shack

miangus · Apr 8, 2022

What old said. I use a little red light with a pig tale. On my FarmAll 400 I can look down the side and see if its charging. I have had bad luck with one wire alternators. I know people love them but that 400 ate several, actually just the regulators. I put in a three wire regulator and no problems.

Geo-TH,In · Apr 8, 2022

I use a light and run both small wires through the ignition
switch after I measured the alternator was a small parasitic drain. Ignition switch fixed the drain problem..

Duner Wi · Apr 8, 2022

I wire mine the same way the GM factory's did and they all seem to work just fine,
I do have battery ignition.
,

Bret4207 · Apr 8, 2022

(quoted from post at 08:33:35 04/08/22) Diode is simple, I buy em at radio
shack

Radio Shack?!!! You still have an operating Radio Shack near you? Lucky!

dwag · Apr 8, 2022

IH part# 548239R1 is another option.

John T · Apr 8, 2022

Actually EITHER a Diode orrrrrrrr a Resistor orrrrrrrrr a small incandescent light bulb (which is simply resistance) will work to prevent
run on when the ignition switch is turned off.

A diode prevents reverse current flow while a resistor or light supplies adequate resistance AND VOLTAGE DROP to stop run on from
backfeeding voltage to the coil.

I have used all 3 and they all worked

John T

ldj · Apr 8, 2022

(quoted from post at 08:24:43 04/08/22) Actually EITHER a Diode orrrrrrrr a Resistor orrrrrrrrr a small incandescent light bulb (which is simply resistance) will work to prevent
run on when the ignition switch is turned off.

A diode prevents reverse current flow while a resistor or light supplies adequate resistance AND VOLTAGE DROP to stop run on from
backfeeding voltage to the coil.

I have used all 3 and they all worked

John T

Well thank all of you. I still don't understand but I don't have to. I'll just do one of the suggestions.

Jim.ME · Apr 8, 2022

You are looking at a 10 or 12 SI Delco type correct? What are you wiring this up on? As well as the ones given, there might be other solutions based on what it is on. There are plug in pigtails available with the diodes already in them. A diesel with a mechanical fuel shut off can be wired direct to the ignition switch, without any of those, as feedback is not an issue. Or an oil pressure switch could be used. If you use an indicator light it must be an insulated socket, two wire incandescent type.

rvirgil_KS · Apr 8, 2022

As stated a diode passes current one way to excite alternator and blocks it the other way to prevent ignition run on.

A common 194 lamp operates at approximately 1/3 amp which is enough to excite the alternator. The ignition system operates at about 4 amps. So when switch is turned off 1/3 amp feedback through the lamp is not enough to sustain the ignition so engine shuts down.

1948CaseVAI · Apr 8, 2022

(quoted from post at 07:56:06 04/08/22)

(quoted from post at 08:33:35 04/08/22) Diode is simple, I buy em at radio
shack

Click to expand...

Radio Shack?!!! You still have an operating Radio Shack near you? Lucky!

I have one a couple of miles from me but they also have a web site you can order from if no store near you, The "express" store near me is in with a hobby shop and is not fully stocked but they do carry lots of components, breadboards, project enclosures, etc.

John T · Apr 8, 2022

ldj, you state I still don't understand Maybe this will help ??

All you're doing with a Diode is allowing current flow INTO the alternator to excite it, but blocking any reverse current flow to the coil
backfeeding it that would allow it to run even with ignition off.........

With a small incandescent lamp (resistance plus a light) or a resistor, you allow just enough current flow INTO the alternator to excite
it yet it offers adequate resistance and voltage drop so the coil doesn't fire after ignition is off.

Easy Peasey right??

Best wishes

John T

buickanddeere · Apr 8, 2022

(quoted from post at 06:30:52 04/08/22) A simple toggle switch will work also. Just can't forget to shut it off.

Why make it complicated with a Cobb job toggle switch or headlights ? Just wire in the proper diode and be done with it .

ldj · Apr 9, 2022

I have wired it and something is wrong, probably me. I run from #1 on alternator through a small light and on to ign. switch. The little light shines with ign. off. Yet I put test light on the ign. and it doesn't shine. Ideas?

Jim.ME · Apr 9, 2022

What did you use for "a little light"? It is not an LED is it? Which terminal of the ignition switch did you hook it to?

ldj · Apr 9, 2022

(quoted from post at 20:05:26 04/09/22)
What did you use for "a little light"? It is not an LED is it? Which terminal of the ignition switch did you hook it to?

No not a LED. I connected to the IGN.

tn terry t · Apr 9, 2022

your light has to have two wires one of the wires to the alternator and the other wire to the ignition

4play · Apr 9, 2022

The diode and bulb perform the same task, just different ways, the diode blocks current from back-feeding to the ignition, and the bulb consumes enough current to prevent back-feeding to the ignition.

I used the volt gauge illumination bulb for this light on my 8n. I seldom drive it at night and it's not a gauge I need to stay illuminated. So if the gauge is ever illuminated then I know I have a charging system problem. My MF245 is diesel with a mechanical shutoff, no need for a diode or bulb.

Jim.ME · Apr 10, 2022

What machine are you installing this alternator on? Gas, propane, or diesel engine? A new wiring or are you tying into old wires? New/rebuilt or used alternator?

ldj · Apr 10, 2022

(quoted from post at 05:51:17 04/10/22) What machine are you installing this alternator on? Gas, propane, or diesel engine? A new wiring or are you tying into old wires? New/rebuilt or used alternator?

It is a m151 army jeep been converted to 12v. Alt is used but it charges fine. I am rewiring the Jeep. I read somewhere problem could be bad diode in alternator. If it is what di8fference does it make as long as it charges and doesn't have parasite draw?

3 wire gm alternator

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