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My car began acting up last night. I pulled over to stop and the engine and lights died. The car restarted easily and ran fine for a mile or two, then tried to do it again downtown. I though perhaps the cut off switch in the ground cable was going out, since the car will run above idle with it off, but that didn't explain the instant re-start. I later noticed the car would sometimes die when I stepped on the brake. Once or twice, the ammeter fluttered crazily. I began to think maybe there was a short in the brake light wiring, or that the brake light load pulled the generator voltage low enough for the engine to die. What it proved to be was that the brake pedal arm under the floor was contacting the battery cable to the starter solenoid when I applied the brakes. This had rubbed the insulation on the cable, which sometimes allowed the pedal arm to short the cable to ground when the brakes were applied, and sometimes not. I moved the cable and taped it, and the problem is fixed, but now the voltage regulator appears to be overcharging. I put the battery on a charger, and will try it again later, but I suspect the intermittent short at the cable has damaged the regulator. The cut out function is working, and the points look like new. Putting a piece of paper between the regulator element points disables the generator and allows the cut out to release. The generator is now behaving like an unregulated 3 brush generator, where as before the regulator did a great job of properly regulating the charge rate, with the ammeter reading dropping to about 0 amps after a mile or two of driving.

Good afternoon...I'm thinking that your battery has been drawn down quite a bit by the short to the break pedal arm. It might take an hour of driving to bring the battery up to the point where the regulator knows that the battery is completely charged. Just my experience with a 31 Model A Ford and a 49 Packard...Others may have differing opinions. Ernie in Arizona

You won't be surprised to hear that having a direct short can cause an overcurrent condition in the regulator. The reason why is because the generator voltage is proportional to:
- engine speed
- field magnetism
The regulator works by controlling the field magnetism, as you know. However the response frequency is only about 200Hz. This is normally not a problem since the battery will handle both voltage spikes and dips (turning off and on loads, respectively) until the regulator compensates.

If you have a direct short to ground then all the sudden you have, instead of 14V calmly charging your battery, you have 14V going straight to ground. A 30A generator will pump out a ton of peak current; but also the cutout relay isn't designed to break 14V or 30A. It's designed to open when there's basically no current flow occurring (= when there's little voltage across it).

So, while the cutout relay should be able to handle that current load closed, you have the cutout relay deciding to open because, directly after the current regulator relay opens and cuts power to the field coils, the generator voltage drops below 12 and the cutout relay opens in the middle of a short condition (11 or 12 volts is still shorted). Oh, and the inductance of the generator armature causes a massive voltage spike across those contacts.


So I would clean your contacts off (on all 3 relays) and try to re-calibrate your regulator. Might need a new one.

Car ('37 120) is 6 volt with a 3 brush generator and a voltage regulator/cutout. All Autolite. The regualtor has 2 elements, one being the cutout. The short must have killed the field current and made everything go dark. I inspected inside the regulator and could see no damage or detect any fried odor. It's very old, but very clean inside and the points look fine. I went for a (hot) drive about an hour ago, and the charging current began to slowly drop until it is now about normal, so it seems the regulator survived the abuse. The standard wet battery needs the levels checked. Cranking speed seems as good or better than before. I left the battery on a low amp charger, and I will check the battery connections and electrolyte level before any more night driving. Most of the wiring has been replaced with original type wiring in recent decades, and seems to be in good condition. I have higher than standard Cp brake light bulbs and headlight bulbs. They draw a fair amount of current, and the ammeter shows right at 0 with the lights on bright. The regulator is rated at 25 amps, but the maximum charging rate seems to be about 12 to 15 amps, which may be limited by the third brush adjustment. I'm tempted to raise that slightly to see if I can get 1 to 2 amps on the ammeter with the lights on bright.