w-31cutlass

When i turn the ignition on, the GEN light is off... when i turn the engine on, the light turns on..
I have charge and everything is alright..
This happend last week... up untill then everything was ok..

I have no idea why it just turned on..
i tripled checked..

what could it be?

InfoJunkie

Try checking the small fuse at the bottom of the fuse box called inst lps

w-31cutlass

This fuse is good.. and the instruments lamps are working.. and if i am not mistaken that is what this fuse is for..

joe_padavano

The GEN light circuit has +12V on one side of the bulb. The other side is connected to the voltage regulator. When the alternator has no output. this wire is grounded, so the bulb illuminates. With alternator working, there is +12V on this wire also. With +12V on both sides of the bulb, the bulb does not illuminate. It sounds like there is a problem at the bulb itself, where the normal +12V feed is shorted to ground instead. This would cause the bulb to be off with the key on and engine not running and illuminated with the engine running. One way to test this is to disconnect the connector at the regulator. Ground the brown wire with the key in the RUN position. The GEN light should come on. Now connect the brown wire to +12V and the bulb should go out. If you get these results, the bulb circuit is working properly and the problem is in the regulator or alternator. If the bulb does not work properly, the problem is in the dash wiring.

InfoJunkie

I ran into the same situation about 35yrs ago. The gauges worked but the fuse was blown. At the time I figured that the GM engineers made the wiring so that if the inst lmps fuse blew the gauges would get power from a back feed through the gen bulb. Changed the fuse and the light went out.

w-31cutlass

I don't get it.. So was it the fuse? Or the bulb?

InfoJunkie

It was the fuse. Sorry sometimes the brain and fingers work on different wavelengths. Have edited my last post.

I also thought the same thing. At this point in my life I had recently developed an intrest in cars and had a previous experience with that gen light. I had taken the problem to a repair shop and they changed the alt & reg and fixed the problem.
A few years later the light came back on and I had aquired the ability to fix my own vehicles and amassed quite a few spare parts. I changed the alt and reg as I had spares but to no avail. After 3 different alts and regs (about a week in time) that pesky light was still on. I ended up changing that fuse and the light went out.

stellar

It is probably a blown fuse. Wireing from alt to bulb is good or the lite would not come on when running and charging. You have an open circuit from the ign to the bulb, most likely a fuse. check them all.

HLS

I just bought a 71 Cutlass Supreme. The Alt looks new but I am not sure it has a built in regulator. The external regulator is still wired in. I read Joe Padavano's reply and did some checking. It appears the bulb circuit is working. I disconnected the brown wire from the reg and grounded it, turned the key on and the light was on. Then put 12v on brown wire and bulb was out. I might also add, I took car to advanced auto and they tested the system. Battery, Starter and Alt checked out OK. I have had no symptoms either. My battery measures about 12.6v and when car is running it jumps up to about 13.4v. Which looks good to me. I tried re-wiring the system like Joe suggested. Unplugged cable from regulator and jumper Blue to Brown, and White to Red. Now when car runs, battery is only 12.4 (Not 13.4 like it was). So am I to assume that the Alt does not have a built in regulator and that maybe I have a partially faulty regulator... in that it causes the Alt to put out 13.4v but fails to put 12v on the brown wire.


What do you think my problem might be. How can I tell if Alt has an internal regulator. I did not see any obvious numbers on the Alt.


Hal

joe_padavano

The alternator on the left is an internal regulator, the one on the right is an external regulator.

HLS

Thanks Joe. I do not have the internal regulator. Based on what you said about the brown wire going to the Gen light... I found out that that terminal was grounded to the frame. When I removed the External Reg. Looked at the underside and that brown terminal was tied to a ground terminal which had a wire attached and went to ground. All I had to do was remove that jumper to ground... and all is well.


Thanks again.
Hal