In the last week or two, I've been noticing that when pulling up to stop light (low RPM) my headlights dim slightly, as do the instrument panel lights.   I suspected that I should replace my voltage regulator, which I did today.  15 minute job.  No big deal.

However, when I started the car, at idle, the GEN light came on and stayed on until I pressed on the accelerator just a bit and the GEN light went off, and stayed off as I drove the car.  

As I approached a stop light, when the RMPs dropped off, the GEN light came on again.  When the light changed and I started to accelerate, the GEN light went off.  The cycle repeated itself.

So, because the wife doesn't know how look it takes to change the voltage regulator :-D, I drove over to the nearby auto parts store, bought a new alternator (I figured because why not..perhaps the old one was beginning to fail), and installed a new one.

When I started the car, the same thing with the GEN light continued:  idle = GEN light.  increasing the RPMs = NO GEN light.    And, it appears the headlights at low RPM dim even more than before I changed the Voltage Regulator and the alternator.   UGG!

I checked the ground on the voltage regulator and the ground appears to be solid.

The only thing I did not change in this circuit was what appears to be a variable resistor of some sort??? See below with the ARROW.  

Any thoughts about what might be going on????  Could it be that the new voltage regulator I installed is bad?


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Here it is with the new voltage regulator.   As I consider (obsess) this problem, it seems to me it either has to be this, the ground, or a bad voltage regulator, no?

Here’s a video of the problem.  Also, should ‘t the GEN light be on when the ignition key is in the ACC (eg radio only) position?

Of course it could be that your voltage regulator is bad, but the only information you have is that the gen light is on.  check the voltage at the battery, and take the battery cables off to see if the engine stalls (b.s. shadetree mechanic alternator test)
is the regulator an oem model with adjustable points?  they can be adjusted
what RPM is your idle?
what about the battery ground to the frame, then from frame to body and frame to engine?  
is it a chinese solid state regulator?  i have one that had the light come on even when the battery was charging because it didn't have the large gen light resistor on it and i had to add it on.

it won't be the condenser on the side of the regulator in the pic usually, but you should try unmounting it from the body and letting it hang.  if the problem goes away, it's shorted.  
then you have to see if you can adjust the regulator points after a few voltage drop tests on the ignition harness with the system running.  also check to be sure the alternator is grounded.  Finally you could have a burnt wire on your ignition switch which is lowering voltage to the regulator

Thanks Mark.   I’ll give it a shot.


Some great tips offered 


I put the old voltage regulator back on and the GEN light has gone off and I’m no longer having the problem.  Go figure.

i’m certain I need a new voltage regulator as the head lights are flickering and dimming slightly at low RPM.

I inspected the black ground wire from the alternator to the voltage regulator and it’s old and the plastic coating broken in several place.  I was considering running a new ground wire and trying out the new voltage regulator again. 
Of course, I could throw in the towel and take the car into my mechanic, but what’s the fun in that?


In most cases just cleaning the grounds on the voltage regulator and removing the terminals in its harness and polishing them will get it working as it should again 

You need to be sliding a flat tool in the harness connectors  to be releasing the individual connectors ( release the metal  bippy there - if you will ) 

That fix  worked in the past for both Jason and myself —-with your same issue 

I think in your case just removing and replacing it must have made a better ground connection and it is now working as it should 

The Gen light will always come on for moments  and then go out —-when the car is started and the RPMs are first low then increase 

When  the Gen light is working correctly—a  low idle RPMs will keep it on —until the RPMs are increased and the light will go out — always comes on for a few seconds when started —-just normal if you idle RPM is correct 

If the Gen light keeps coming on at an idle — your idle is to low 

There is a fuse housing on the passenger wheel well —for the Gen light just so you know —for the future 

With our year Cadillacs the first thing to do with any electrical problem —-is ALWAYS -  to be cleaning the grounds involved and 98% of the time that will fix the problem 

Ground connections get intermittent and build resistance  due to cars age 

Do clean the negative battery cable to the frame —under the battery tray to shinny metal —as that is the Mother ground connection 

Get the regulator connections cleaned up and you should be good to go —- Fixed ! 

I would keep the old regulator and a new alternator is always a good thing for future long term  performance 

At an idle-  on a volt meter -  you should be putting out 14 volts —at the battery when the charging system is working correctly 

Love the easy cheep ( no parts ) fixes myself—- always 

You and me have an obligation —-to be keeping your outstanding restoration rolling down the road so you and all others around you can enjoy your great  64 Classic Antique Cadillac ( ICONIC ! ! )

Keep an eye out for any—  Loose  NUTS—. ( and wiring ) as I recently had to do with my Starter solenoid ——HA - HA !! 




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