Thread: Gen Light
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Old 07-03-2017, 06:19 PM
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Originally Posted by 9310alloy View Post
Dave , I have to disagree on how to test generator / regulator output.

"B" circuit generator / regulator (original Thunderbird).
You NEVER want to jump battery terminal to field terminal at the regulator with the wires attached to the regulator. This will burn out your voltage regulator field contact system in your regulator.

Testing your generator / regulator for output :
Remove field wire from voltage regulator and with engine running at 1200 to 1500 rpms. Touch the field wire to armature terminal at regulator for a few seconds. If the voltage increases to 14 to 15 volts. The voltage regulator is bad. No change in voltage the generator is bad or wiring issues. This test is unregulated so do not run for more than a few seconds to read your volt meter.

Always check wiring for a good ground (no voltage loss) between regulator and generator , frame , block , battery.

Polarizing your "B" circuit generator :
Engine off. Disconnect the field wire from your regulator and touch / flash to battery terminal on your regulator.

Mike, your suggestion is plausible BUT it doesn't get the job done.

Mike, study the wiring diagram and notice that the armature and field are already connected via both normally closed contacts. If you go through your procedure, nothing has changed.

I'm trying to determine if the generator is capable of outputting charging current.

Since I suggest adding a temporary jumper from +12 to the field with the engine running, there is nothing that can be harmed. Remember, during normal operation the generator's armature outputs 30-amps at ~14-volts. All that is impressed upon the field until either (voltage or current) relay contacts open.

ALSO, the GEN light is already connected to the armature (and field coils) as soon as the key is turned 'on' through both the regulator's N.C. contacts. This 'tickles' the armature and makes enough magnetism (in the correct direction) to start producing current when the armature windings pass through the field magnetism. There should be NO reason to 'flash' or 'polarize' a charging system with a GEN light. Case in point: How many Squarebird owners had to polarize, even after 50 years?

DeanJ, you should have a resistor across your GEN light wires for two reasons; to shunt that small amount of current that makes your light flicker but more importantly... If your GEN light burns out, the alternator will not know the key is on and it will stop charging. The resistor will pass enough power by itself to keep the alternator going. Even with the resistor, your GEN light should work as you would expect. - Dave
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