How To Bench Test Your Generator

Battery charging issue seems to be a common problem with our vintage British cars. Here the Moss Motors Tech specialist walk you through checking your generator to see if it is functioning properly. Does the problem lie in the generator, wiring or voltage regulator. This video will help you eliminate one of the culprits. See our How to Test Your Voltage Regulator to get the rest of the story.

While this generator looks like it belongs in a museum, you might have one just like it in your Classic British Car.

We have two issues.

1. These do occasionally fail like any other mechanical part in your classic car.
2. The people who know how to test these are going the way of the dodo.

You can test your generator yourself. You can do it in your car. Without a test bench. Today, we’re going to do two tests to show how much you can learn with little or no official test equipment. To avoid the noise, and to better show you what I’m doing, I’m going to work without the car. I’ll be simulating what you will do with your generator installed in your car.

To begin, you should have your generator installed in your car. If it hasn’t been polarized, it would be a good idea to polarize it. (That will take about thirty seconds.) Let’s have some fun and test with an old school method and then a method from a not quite so old school.

Fred Flintstone Method
I have no volt meter, no ohm meter, no amp meter, no test light. Does my generator work?

1. Engine off. Remove the belt.
2. Remove the two wires from the generator. Store safely. No power connections, but it has ground.
3. Put a jumper between the two terminals.
4. Jumper to brown wire on fuse box.
5. Touch jumper between two terminals.

Deciphering the results… dead = dead     live = probably OK

Wright Brothers Method
I have a volt meter. I don’t just want to know if the generator works, I want to know if it works well enough.

1. Belt on.
2. Remove the two wires from the generator. Tape off the wires. No power connections, but it has ground.
3. Put jumper between two terminals.
4. Connect voltmeter
5. Start. Fast idle. RUNAWAY DANGER. DO NOT SPOOL UP
6. At least 14V. Don’t let it get above 18V-20V.

NOTE: These tests eliminate the car’s native wiring. If there’s a problem, it’s probably not in this.