Wiring GM 3 wire - Idiot light not lighting

Thank you in advance for your help..

I have a GM 3 wire alternator. I have connected it as shown in the pic below. I have the exciter wire going to the accessory on the ignition with a idiot light in between. I have tried two alternators and neither one will light the idiot light up. Any thoughts?

Once again thank you for your time!

 

What do you have the other lead of the light going to?

 

Make sure you have it wired like this

 

The #1 exciter wire goes to the ignition/run post on the switch, not the accessory.
The #2 sensory wire should go to the relay, or main voltage distribution point, to allow the alternator to provide +/- 14.4 volts to the system, not just to the rear of the alternator.

themoose, you beat me to it!

 

The other wire is going directly to the starters + wire that goes to the battery.

 

I am in no way saying you are incorrect, but the accessory post and the ignition post both have a positive when the car is started and running. I didn't hook it to the ignition post because I didn't want it on the same post as the coil +. Is there a difference between the run and acc?

Thanks again!
-Ronnie

 

Let's clarify what "the other wire" is. Pin #2 on the alternator is a reference voltage wire, and is what the alternator uses to determine how high of voltage it needs to produce. This wire should be connected as close as possible to the + post on the battery. In order for the battery to be properly charged, the voltage at the + battery post needs to be somewhere near 14 volts. (13.8 to 14.4 is the typical accepted range for maintaining a decent charge on a 6-cell lead acid battery, 2.3 to 2.4 volts per cell.)

Pin #1 is the charge indicator, or idiot light. The proper connection is from pin #1 to one side of the indicator light, and the other side of the light needs to be connected to the IGN/ACC side of the ignition switch. Pin 1 provides a path to ground when the alternator is NOT charging, so that when you turn the ignition key on, the indicator lights up. When the alternator begins to charge, Pin 1 goes from gound to the charging voltage, so that there is the same voltage on both sides of the indicator lamp. Same voltage on both sides of the indicator lamp means no current flows through the lamp, and it goes dark.

 

Simple test- key on, unplug from alternator and ground #1. Light come on? Wiring OK. If light didn't come on you have a issue between ignition switch and alternator. And I agree it should be connected to the accessory terminal on ignition switch.

 

^^^ as he said, the lamp is lit with the key on but the engine NOT running.
The lamp goes out with the engine running (shows the alt is charging).

Is the battery being charged with the engine running?
What type bulb are you using? I use a T1893 (14 volt auto lamp).
Is the bulb filament good?

 

The only thing different about my scenerio is the plus wire does not go all the way back to the battery. It loops from terminal #2 over to the battery connector on the alternator It them goes to the positive on the starter instead of the battery. Terminal #1 is connected to one side of an indicator light and the other side of the light is connected to the ACC.

I think I am going to take the alternator off tonight and have it officially tested.

Thanks for your help everyone. I will update again once I have the indicator light working.

-Ronnie

 

I am using one of the standard 2 wire lights that typically come with a set of gauges. It came from an older broken gauge. I tested the light by running fron the ACC to ground after the light didn't come on wiring the alternator.

Thank you all for your help. I am sure I will have it figured out tonight. I will update again at that time.

 

There has to be an initial resistance in the alt light circuit. So whether you use a lamp or a resistor, there needs to be resistance to establish field reference.

 

Jump a test light between the two terminals, not the main power line. With the engine running you should see the alt begin to charge

 

I will try this.

Thanks!

 

You've only got to momentarily jump them, then it should be charging. 1 wires are so much easier!

 

Except when you cannot train your customers to rev-up to 2500 to get the alternator to engage, especially on a bagged car, blame all the "charging issues" on you, trash-talk your work, and write bad Yelp reviews about your business over it. One-wire alternators easier? Hardly. I no longer install them.

 

A bad diode trio can cause the light to not come on. or to be on with key off.

 

I prefer to hook the light up to the acc circuit. that way the light will come on when the switch is turned to acc and remind you to turn it off.

 

Maybe your ignition switch doesnt have +12v on the ACC terminal if the switch is in the ON or RUN posistion? Did you check to see if it does? Did you verify +12V on the ACC terminal when the switch is in the ACC position? Maybe just a bad ignition switch especially if you have tried two alternators already. I wire that style alternator with the jumper from pin 2 to the stud on the back of the alternator and they work fine.

 

The difference between run and ACC: Both are powered when switch is in RUN or on position, Run pole stays hot while key is turned to START but ACC pole goes off til key is returned to RUN. All poles off, except ACC when key is in ACC position.

As stated before, the idiot light gets its ground from the alternator when not charging.

 

The light is incandecent? or LED?

 

Bulb dead? Alternator charge at all? If so, check the wiring to the bulb to see of the two leads are shorted to each other. If bulb is dead, the alternator will not charge.

 

This sounds like the opposite of what I read. That the wire from #2 pin shold be connected to a remote circuit like a tail light so that it reads voltage demand from the whole car not just the battery.

But who does that?? GM maybe? I jumpered mine like in the first diagram.

 

You want the alternator to deliver the proper charging voltage to the battery, so the reference lead ideally should be right at the battery post, or somewhere else that doesn't have a voltage drop. Connecting it to a remote circuit like a taillight would most likely mean you'd be overcharging the battery, since there would be some voltage drop way back there at the taillight.

Plus you'd have to have your lights turned on for the alternator to function properly.

 

You make some good points, Ebb. You can read all kinds of crap on-line.

 

As promised I am back with an update. Connecting to the battery positive on the starter and ACC did not seem to be an issue. I went through all of it to insure I had not done something wrong. After pulling everything out I found a bad / corroded wire. It appears someone might have punctured it with a test light some time ago and the wire finally went bad.

Thank you all for your help!