Polarity question
- Thread starter dam555
- Start date
Doug Money
Senior Member
The ammeter leads need reversed and the generator needs to be repolarized. Here is instructions I found:
To change to Negative Ground
Disconnect the harness wire to the generator cutout and don't let it short to the car.
You will rotate the battery. Hopefully the battery post connectors are correct as one is normally larger (I don't recall which). I usually leave the positive off until I'm through tinkering.
You will have to re-polarize the generator. Use a piece of wire long enough to reach from the battery positive post to the generator and touch it to the nut that connects the cutout to the generator. (Not the output connection on the cutout.)
Remove the above wire and reconnect the wiring harness to the cutout. Reconnect the battery positive connection if you chose to leave that off (for safety)
Start the engine and check with a voltmeter that the generator is indeed outputting positive voltage measured at the nut ahead of the cutout. You can do this before you rev up and engage the cutout. (You could very briefly run the engine with the battery positive still off to check polarity).
NOTE: some digital meters don't read correctly near a model T due to interference from the ignition system.
You may have to reverse the connections on the ammeter to get it to read in the correct direction.
You DO NOT EVER want to run the engine without a battery properly connected because there is HIGH RISK of permanently damaging the generator.
To change to Negative Ground
Disconnect the harness wire to the generator cutout and don't let it short to the car.
You will rotate the battery. Hopefully the battery post connectors are correct as one is normally larger (I don't recall which). I usually leave the positive off until I'm through tinkering.
You will have to re-polarize the generator. Use a piece of wire long enough to reach from the battery positive post to the generator and touch it to the nut that connects the cutout to the generator. (Not the output connection on the cutout.)
Remove the above wire and reconnect the wiring harness to the cutout. Reconnect the battery positive connection if you chose to leave that off (for safety)
Start the engine and check with a voltmeter that the generator is indeed outputting positive voltage measured at the nut ahead of the cutout. You can do this before you rev up and engage the cutout. (You could very briefly run the engine with the battery positive still off to check polarity).
NOTE: some digital meters don't read correctly near a model T due to interference from the ignition system.
You may have to reverse the connections on the ammeter to get it to read in the correct direction.
You DO NOT EVER want to run the engine without a battery properly connected because there is HIGH RISK of permanently damaging the generator.
RonC
Well-known member
To polarize a generator with a stock type cutout, just take a pair of pliers and momentarily connect the two cutout terminals together with the handles of the pliers. You can do this with the car off or running.
If for any reason you ever need to run your car without a battery, ground the terminal that comes out of the generator housing. Tie a piece of wire to that terminal and connect it under one of the cutout mounting screws. This is to prevent the generator from producing full output which will overheat the generator melting the insides.
If for any reason you ever need to run your car without a battery, ground the terminal that comes out of the generator housing. Tie a piece of wire to that terminal and connect it under one of the cutout mounting screws. This is to prevent the generator from producing full output which will overheat the generator melting the insides.
CharlieB
Well-known member
Dam: you didn't say which way your amp meter needle goes with the eng. running. To the left is discharge to the right is charge. You may not have to do anything besides reversing the battery connections. (It's the first step any way). My '27 had the same problem. Some backyarder may have told the former owner the A was pos. ground so the T must be too. My meter went to the discharge side. I checked the batt. and it was pos. grounded. I reversed the batt. and the needle swung to the right (or charge side) and I never did anything else to the system. For whatever reason it didn't harm the gen. at all. Hope the same works out for you.
