dnohe

All

I'm looking for advice to diagnose a recurring GEN light illumination situation on a 72 Cutlass Supreme when the car is turned off.

Several months ago we noticed that the GEN light will illuminate when the car is turned off. Initially We figured it to be the alternator (I could pull the plug on the alternator and the lamp would be extinguished). The rebuild worked for a short while then the symptom reappeared. However, this time pulling the plug would NOT extinguish the lamp. Then we noticed that sometimes the lamp would go out (especially if I slammed the car door shut) - leading me to believe it may be a faulty ground.

I replaced the battery today (it was time) and new battery lead connections. I'm now believing in a loose ground connection elsewhere. No idea where to start....Any suggestions???

The GEN light only illuminates when the car is turned off - and stays illuminated. Not able to determine any other symptoms or possible causes.

Thanks in advance.

Seff

The GEN light works by having 12+ through the ignition switch. When the generator side is grounded, the bulb lights up. When the generator side supplies 12+ (IE the generator is working), the bulb sees 12+ on both sides and thus a net 0 volts - which means it doesn't light up.

Does your car have a voltage regulator?

1970VistaCruiser

Did you ever get this diagnosed I have the exact same issue with the same car?

bsettlefl

I"m not sure if this is still open or not, but I have the same issue and don't see any resolution here. I thought at first it was the ignition switch and replaced that. At first it seemed to fix it, but only temporarily. It isn't constant, and when it happens I haven't found any consistent way to make it go out. And last night it died while driving, I believe ignition related. Do these have an external ignition relay?

oldcutlass

The gen light has 12v fed to one side from the ignition switch on circuit and the other side is fed off the brown wire from the voltage regulator. If there is a deviation in voltage the gen light will light. Usually when the gen light is bright its a voltage regulator failure.

bsettlefl

So if the GEN light stays on when the ignition switch is off it has to be getting power still from somewhere, and ground or a lower voltage through the voltage regulator. Sounds like I am going to find either insulation wear or a butchered accessory wiring job somewhere.

Thanks

oldcutlass

Yes, you need to take some voltage measurements at the light to see which direction to go. Depending on which wire has the voltage is going to be the next step.

droldsmorland

First, verify all electrical connections at the battery and alternator are good. Next load test the battery. If it passes move on.
This is a 72 so it should have an internal voltage regulator inside the alternator. not mounted to the firewall..correct?
True or false, the gen light is illuminated with the ignition switch in the off position engine NOT running?
If this statement is correct, disconnect the number 1 and 2 connectors off the backside of the alternator. Does the light go off? If yes its a bad rectifier bridge in the alternator.
If the light stays on there's a short in the #1 & #2 wire harnesses.

green1972

A 72 Supreme has a external voltage regulator

Gpc1

Had an issue with gen light staying on dim while running, turned out to be bad circuit board behind speedometer
this could be another place to look if all else fails