1976 Cadillac Deville Generator Dash Light Still On?

[EAM 17806]

With two NEW alternators installed the dash light still comes on.  What's going on? All belts are properly installed and hookups are all okay.  EAM

[TJ Hopland]

Now days the new parts would be the most suspect but assuming they are not the issue I would be checking fuses.  Specifically one that should be labeled 'gauge/trans' which I think is a 10 amp.  If its blown and you replace it and it blows again I would be checking the wire that goes into the transmission just above the pan and its route to the side of the carb then the wiring around its switch on the side of the carb.

That circuit also runs the buzzer which among other things gets tangled up with the seat belts so that is another place for things to go wrong if at some point in the cars history someone did want to use the seat belts and didn't want to listen to the buzzer.   I have seen lots of poorly thought out and executed mods to that circuit cause issues later in the cars life.   

[EAM 17806]

With two NEW alternators installed the dash light still comes on.  What's going on? All belts are properly installed and hookups are all okay.  EAM

Now days the new parts would be the most suspect but assuming they are not the issue I would be checking fuses.  Specifically one that should be labeled 'gauge/trans' which I think is a 10 amp.  If its blown and you replace it and it blows again I would be checking the wire that goes into the transmission just above the pan and its route to the side of the carb then the wiring around its switch on the side of the carb.

That circuit also runs the buzzer which among other things gets tangled up with the seat belts so that is another place for things to go wrong if at some point in the cars history someone did want to use the seat belts and didn't want to listen to the buzzer.   I have seen lots of poorly thought out and executed mods to that circuit cause issues later in the cars life.

All the other gauge dash lights are working fine; wouldn't this generator light be out too if it were a fuse problem?  EAM

[bcroe]

I would at least double check the 5A GAUGE fuse.  If OK, I would slap
in an alternator known to be good (previously tested).  And use a clamp
on to check alt output current, put on some loads (lights and blower). 

Bad alternator diodes can light the GEN light, even with good or partial
output.  They can be checked with the alt apart.  Another cause is
weak wiring, causing a lot of voltage drop.  good luck, Bruce Roe

[TJ Hopland]

Its kinda a wacky circuit because when the alternator is spinning its basically sending 12v back to the bulb so it can back feed anything that is on the same fuse as the gen light which is most of the other indicator lights, gas gauge, buzzer, and the downshift circuit for the transmission.

You could unplug the small plug on the alternator and see if everything else still works.  Gen light should go out but the rest of the stuff should still work if the fuse is good.

That seat belt circuit is also a good way to pick up a lot of unexpected interactions because that buzzer ties into things like the door switches that work off ground so it only takes one thing to be out of place out of like a dozen things to cause all sorts of interactions.     

[1776-1976-Eldo]

I will second checking the alternator. I had 2 that were bad for different reasons. It is very easy to take the alternator apart and ohm out the components. If 1 of the 3 legs on the diode trio is out, it will dim light the generator light. I was still getting good power out of the alternator even with a bad trio leg.

[EAM 17806]

I will second checking the alternator. I had 2 that were bad for different reasons. It is very easy to take the alternator apart and ohm out the components. If 1 of the 3 legs on the diode trio is out, it will dim light the generator light. I was still getting good power out of the alternator even with a bad trio leg.

It turned out the problem was the fan belt; it was on tight but needed to be replaced because it was slightly slipping because of too much wear.  I'm glad that's all it was!  EAM

[The Tassie Devil(le)]

Good news.

Bruce.

PS.  So, do you now have two new Alternators as spares?

[EAM 17806]

Good news.

Bruce.

PS.  So, do you now have two new Alternators as spares?

No, I had to return the ones in warranty to the parts store, rightfully so.  EAM