I have a 351C in a '53 F100 with an aftermarket alternator and standard voltage regulator. The system is not charging. How can I test weather it is the alternator or the regulator?

Thanks
Gary:

 

I am assuming your "aftermarket" alternator is setup the same as a stock alternator? You should have 3 terminals on the back, "s", "f", and the large battery output wire.

First, to make sure it's not charging, measure the voltage on the battery with the truck off, and then with the truck running. The voltage should be higher on the battery with the truck running if it's charging.

The next test is to take the voltmeter, and with the truck off, probe the large output wire on the alternator, with the neg meter lead on the neg of the battery. You should have 12 volts on the large terminal. If not, then you have a wiring problem with that wire.

If that checks ok, then take the "f" wire off the back of the alternator and tape it. Get a scrap piece of wire, and hook it to the "f" terminal of the alternator. Start the truck, and then with the voltmeter on the battery, touch the "f" wire to the positive of the battery. If the alternator is good, the voltage will jump up on the battery, and you also may hear the engine slow and the alternator may start whining.

 

Thanks Dave I will try the test. I already tested the battery with the truck running and it registered only 12 volts. I will try the wire test. Thanks for your input

 

if the ALT is bad, try changing the brushes, about $6 at NAPA