Generator issue? 55 DeSoto Fireflite

Did you polarize the regulator after you installed it ?Try polarizing gen& regulator again.The car does not need to be running.

Your first comment is that the car doesn't hold a charge.... did you have the battery tested? "Holding a charge" would be a function of the battery.

Otherwise, I agree that I think you have a generator issue. The regulator doesn't require polarizing. That is a procedure to magnetize the field coils in the generator with the proper polarity, and residual magnetism will remain in a benched generator for at least a few months, if not longer.

When you ordered your new regulator, hopefully your parts person knew you were dealing with positive ground.

Here's a video that I found really well done. Your generator has a larger "A" terminal (armature) and a smaller "F" terminal (field). And remember that your car is 6 volt positive ground as you consider the values that the narrator gives in the video.

https://www.youtube.com/watch?v=RjLW_eb3D-c

I love this video! It makes sense to me, now to remember this information as needed!!

Standard Parts Corp recommends that any new voltage regulator of the type used on our cars should be polarized after installation,before the vehicle is started.

Thanks all...took the recommended steps, and the car runs fine - in the day time. As soon as I turn on the headlights, engine does a slow fade, and I have to them them off, at which point everything goes back to normal. Needless to say, I'll stick to day time driving until this is reolved. Any thoughts/ideas are wlecome.
thanks
Joe

Joe,
It sounds like you have a generator "output" issue rather than a voltage regulator problem.
Your amp gauge should show a positive charge after starting which should stay on the positive side once you turn on the headlights. If it goes negative it means that the generator can't supply the necessary amperage to run the car and the lights.
This could be just a case of worn brushes and commutator on the armature.
Your mechanic (or parts store) can run a charging system check to see what the system is capable putting out.
Also with 6 volt system, all of the connections have to be really clean or the amperage will be reduced by the corrosion. This is a good place to start.
Keep us posted with your progress.
Best regards,
Geoff

Thanks Geoff - appreciate the suggestions, and will give those a shot this weekend. Amp gauge definitley skews negative as soon as the headlights come on, and returns to the positive side once they are turned off.
I'll send an update as to the progress, and thanks again.
Joe

I would think that even if you had fully charged battery and turned on the lights, you would not experience an immediate degrading of the car running. A battery should be able to run a car for a while even with the lights on.

Your description says that you experience a fading of the engine and have to turn the lights back off. Is that nearly an immediate event?

It sounds to me like the headlight circuit is taking an extraordinary draw on the system to the extent that the ignition circuit is significantly robbed of enough voltage to fire the points.

Can you put a meter in the headlight circuit and see what kind of amperage draw you're getting with the lights on?

Tim,
I see you were able to help on a generator issue previously. Maybe you can help on this one?I have a 32 Desoto 6 SC. When running w/o any lights on it shows 5A charging on the ammeter. When running if I hit the brake lights- it goes to zero(this test w engine off goes to minus 5A). When running if I turn on the parking lights ammeter goes to zero(minus 5A if not running). When I turn on the low beams while running, it goes to minus 5A(minus 10A if not running); and with hi-beams goes to minus 10A on the meter(minus 15A if not running).
Of course its a 6V positive ground system. I have installed a complete new wiring harness, and believe all the connections are clean. I believe ground is good, as I ran grounds separately from each of the 4 lighting hubs to the chassis, and ran a big ground from block to the frame.
So I am thinking generator may need new brushes or some sort of service? If so- are local starter/alternator shops going to be able to do this? Is there some other test I should do to troubleshoot? Are the current draws in the ballpark or excessive?
Any ideas or guidance for a person baffled by electricity would be appreciated.

Electricity is voo-doo to me, too.

Have you watched this video and considered if you can do any of the self tests to check your generator's output?

https://www.youtube.com/watch?v=RjLW_eb3D-c

It sounds to me as if you are right, the generator needs a tune-up. The behavior seems normal, only that the generator isn't providing enough current to overcome the draw of your lighting accessories.

Is the car at idle when you experience these specs you're stating, or is that driving down the road? A generator doesn't really put much current out at low rpms, which is a major frustration and one of the reasons that people choose to do an alternator conversion. Does the charging rate change at higher RPMs?

Does your car have a more conventional voltage regulator, or just a cut-out? The cut-outs can be adjusted, too.

I've gone from working on our generators as far as I can (clean up and bench test to see if a generator will motor...) to taking them to a friend that is still teaching at Mac College, to having discovered a starter/alternator shop in Hutchinson, KS that I can carry both the generator and the regulator in and walk out with a setup that has been set to work together. I've been pleased with B&B Auto Electric in Hutch and would offer them as a source to send your stuff out in you end up doing that. Not that there aren't other provides, these guys are just 25 miles down the road for me.....

Hey, Thanks for the ideas! Yeah I watched some of the videos and from my testing decided as you suggest, it just wasn't putting out enough power.
So when all else fails, read the instructions! Turns out the owner's manual had instructions for how to set the output of the generator. There's a "third brush" that can be rotated to change the output. So with the engine running and lights on, I adjusted the position of this brush and watched the ammeter (at cruising speed, not idle). I rotated it until I got to slightly charging with the brights on.
I think eventually I will need to get the brush replaced or adjusted because in the 1.5" swing of the adjustment, the change to the output all occurred in the last 1/8", and even 1/16" past where I stopped was overdoing it, hitting plus 20A with the brights on. Pretty touchy.
I need to do some shakedown runs to confirm I have got it. Maybe I will drive to one of the local generator/alternator shops. And yes, this one just has the cutout.

Update- Put new brushes in, and adjustment to generator output came back, i.e. I had more gradual adjustment/range. Got it set and all is good.
A comment- my biggest wiring problem was the headlight receptacles. The contacts to the bulbs are basically a ball of solder on the end of a wire, and the balls of solder were sloppy and contacting the sides of the receptacles and shorting/blowing fuses. Finally took the dremel to them to reduce diameter and insure no contact at the sides. Problem solved- pretty basic, I just was surprised that the reproduction "new" receptacles were so poorly done.
Now I have to take it out at night and assess whether there's actually enough light to feel safe driving after dark!

Posted by: @joeduggan

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I have a 55 Fireflite, and recently had the voltage regulator replaced as the car was not holding a charge. Last night, I took the car out for a drive (about twenty minutes.) As I headed home, the lights began to dim, and eventually the engine started to fade/cut off. I turned the lights off as I approached the driveway, and the engine came back to life. I'm guessing this might be a genertor issue? The charge/discharge indicator was not moving to the charge side, so that's my best guess. I'm not a mechanical wiz, just know enough to be dangerous. Any thoughts or suggestions would be appreciated.
Thanks
Joe

Grammar help–––ISSUE is not a replacement for PROBLEM. You were not issued a generator.

To save building cost, modern motor vehicles lack an ammeter, an important gauge. If not only an idiot light, a voltage meter is provided but that does not tell you the whole function of the charging operation. An ammeter–––a zero-centered ammeter tells you the state of battery charging–––whether the battery is charging, idle, or discharging.