1972 Cutlass Supreme. When I shut off the car the GEN light illuminates and stays lit. It is not on when the car is running. I had this issue before and had the alternator serviced and that helped for a while. Also when I had the issue before I could unclip the plug on the alternator and the lamp would go out. When I try that now, the lamp stays lit. Only way to extinguish is to pull the cable off the battery terminal.

Any suggestions before I take it back up to the alternator shop?

Thanks in advance

 

From what memory serves me, it could be a bad diode in the alternator causing this to happen. It may not hurt to take it back to the alternator repair shop to verify.

 

A bad diode in the alternator will definitely cause this, but he said when he unplugged the alternator connector the light stayed on. If it were a diode, unplugging the alternator would break the circuit and the light would go off.

I have no idea what would cause this issue.

 

I'm thinking a ground wiring problem.

Eric

 

Bad regulator. Unplug it and the light will probably go off.

 

X2 on the voltage regulator.

 

Hi Fun71! The thick red wire that goes to the back of the alternator goes to a rectifier bridge that also has diodes in it. But yes, it was late last night, holy stuck contacts Batman! Voltage regulator can be bad as well, is it the mechanical type on the firewall? How easy one forgets in the day and age of electronics.

 

Yes, change the regulator and you should be good.

- Eric

 

I'm thinking it was a grounding issue. The battery terminal may not have been making good contact with the threaded post. I put in a longer threaded post and its making much better contact and now my GEN light isnt coming on with the car off. Coincidence - maybe, but for now, issue resolved.

Thanks for all the suggestions.

Dean

 

If the negative battery post was not making good contact, you would have nothing. Coincidence.

 

I am battling the same issue right now on my 72 Supreme. The only way the light will go out is to disconnect the voltage regulator harness or disconnect the battery. I had purchased a new regulator last year and this issue just started up when I got the car out this past week from storage.

Regulator Replacement?

 

I feel your pain. Replaced the Regulator. Rebuilt the alternator. Replaced battery and battery cables. Same results. I'm convinced there is a short elsewhere in my vehicle, but not in the know of how to diagnose and find it.

I resolved by adding a battery cut out switch (for about $20) and I flip the switch at the end of the night and when I put he car back in storage. It wont "fix" the issue, but its a manageable solution.