1950s Generator "idiot" light stays on

[Bronze]

Working on a 1956 Coupe. Generator light on all the time. 12.5 volts at battery with engine off 13.5 volts with engine on so it seems to be charging. If I disconnect brown "gen" wire from both generator and regulator "idiot" light goes out, as it should, no ground. If i connect back to generator i get a strong red light , as i should.If I connect brown wire to regulator only i get a dim red light. not sure if that is correct. The regulator is providing a "weak" ground at "gen" post. Anyone more electrically inclined that can advise if my tests indicate anything useful and what my next steps should be? regulator looks perfectly new both inside and outside. and yes i have checked the workshop manual. too complicated for me....

[TJ Hopland]

I don't know the gen systems as well as the alternator ones but if its the same sort of circuit I would be looking at fuses that feed dash stuff.  With the alternators if that dash fuse blows the alternator ends up back feeding other things on the fuse so the light lights. 

[J. Gomez]

Martin,

It is common for the "GEN" light to be dim or flicker when idle in low RPMs. If you increased the RPM a bit does the light goes off?

The generator do not charge the battery during low idle RPMs and if the battery a under load (weak, low charge) you will have the GEN light on. If however the light does not go off when you raised the RPMs then you have an issue with either the generator or regulator.

The generator could produce a higher voltage (at idle) than what the battery has but not enough to pull the voltage regulator relay (open contacts), so there would be a difference of potential (voltage) between the "GEN" (A terminal on the generator) and "BATT" (main 12V source from the battery) terminal at the VR. Since the "GEN" light is wired between the main positive 12V (pink wire) and the "GEN" terminal at the VR (brown wire), the "GEN" brown wire at the voltage regulator would be more positive than the "BATT" terminal causing the light to dim. 

[Jeff Rosansky CLC #28373]

Is this a new problem, or going on for a while, or are you waking up a car that has been sitting?
J Gomez has helped me in the past so take his advice. But I have a couple of things to add.
It may be worth polarizing the generator if it hasn't been done in a while. I don't really know what that does, but I have seen it help on things in the past so it can't hurt-- Besides, who can resist intentionally making sparks??
I would also clean all contacts at the generator and regulator. You may also want to check the regulator ground and the point contacts in the regulator. It may be that the points are welded together or there could be a piece of crap in there that doesn't allow them to fully open. It usually stays pretty clean in there, but still worth the look.
I had a fuse issue on another system at 1 time so you may want to replace that. It tested ok, but the metal was loose from the glass tube causing intermittent contact.

[Lexi]

Yes, Jose is the man and as I say, one of the "Cadillac Gods". Good advice from Jeff to polarize the Generator as a "just in case". Clay/Lexi

[TJ Hopland]

Polarizing is basically back feeding power into the generator.  This energizes the internal coils/electromagnets which then magnetizes the metal internal bits.  For a generator to get started it needs this permanent (non electro) magnet properties.  Over time especially non use the internals loose their magnetism. 

The polar part of the term is depending on the polarity of the power you back feed into it which way the parts get magnetized and its that polar (north or south) relationship that makes it a positive or neg ground unit.           

[Bronze]

Thanks för all replies. It is a resurrection that i took over. Polarizing is done. Light will not go out by revving. Guess i will need to get deeper into the regulator....

[Jeff Rosansky CLC #28373]

Thanks för all replies. It is a resurrection that i took over. Polarizing is done. Light will not go out by revving. Guess i will need to get deeper into the regulator....

I ended up having to put a new regulator on our 55. It was out of adjustment and needed a little tweaking. BUT you don't adjust the point gap like the old ones, you adjust the spring tension. I didn't find that out until after I had fiddled with it a while, returned it, got another one, had the same problem, and finally contacted the manufacturer.
So, if you end up with a new regulator that needs adjustment, contact the manufacturer to see how they say to adjust it.

[dn010]

I've had regulators lose their "ground" contact with the body before. I tested this by running a jumper from the regulator body to the negative battery post and a lot of times all my troubles would clear up. My be worth a shot to test.