Farmall H Alternator Wiring

OK all help me out here. I converted our 6V positive ground model H with generator to 12V negative ground. I wired it per the attached pic I found on this site. I have tried two known to work Delco 10SI three wire alternators, both with dummy light and or diode and it will still not charge.... I have checked and double checked all the wiring and made sure there are good connections. I have had others check the wiring to make sure I followed the path correctly and still I cannot get this guy to charge. WHat could be my issue?

Explain how your checking to see if it does charge??? If going just by the amp gauge it could be bad and that would cause odd problems.

Several things to check:

1 - Is the ammeter indeed working? Turn on the lights or ignition with the engine off. The ammeter should show discharge. If not, replace the ammeter. Alternatively use a voltmeter connected across the battery terminals to check alternator operation (12.6 volts or less = no charge; 13 volts or more = battery is charging.)

2 - Check voltages at all 3 alternator terminals with the ign "on" and the engine stopped. You should see 12 volts at all 3. If not there's a wiring problem.

3 - Could be the alternator is spinning too slow to "turn on" the regulator. Start the engine and run it up to maximum RPM for a couple seconds. If it starts charging it will continue to do so after you slow it back down. (This is normal for the 10SI alternator.....)

4 - Verify the alternator is indeed good. With the engine running at half throttle, use a small screwdriver on the test tab inside the D-shaped hole in the rear of the alternator to ground it to the the alternator case (photo below). If the alternator now charges either the internal regulator is bad or there's a wiring problem.

1 - Is the ammeter indeed working? Turn on the lights or ignition with the engine off. The ammeter should show discharge. If not, replace the ammeter. Alternatively use a voltmeter connected across the battery terminals to check alternator operation (12.6 volts or less = no charge; 13 volts or more = battery is charging.)

The ammeter is working, it reads discharge with the ignition switch on with the tractor running or not running. With the tractor off and the switch off it goes back to zero. I have used a volt meter across the battery terminals with the tractor on and off, it reads 12.6 either way.

2 - Check voltages at all 3 alternator terminals with the ign "on" and the engine stopped. You should see 12 volts at all 3. If not there's a wiring problem.

Have not tried this, but will do so.

3 - Could be the alternator is spinning too slow to "turn on" the regulator. Start the engine and run it up to maximum RPM for a couple seconds. If it starts charging it will continue to do so after you slow it back down. (This is normal for the 10SI alternator.....)

I did take the tractor out for a ride with it at full throttle in 4th gear, but the ammeter still read discharge.

4 - Verify the alternator is indeed good. With the engine running at half throttle, use a small screwdriver on the test tab inside the D-shaped hole in the rear of the alternator to ground it to the the alternator case (photo below). If the alternator now charges either the internal regulator is bad or there's a wiring problem.

Have not tried the test you mentioned and will do so. The first alternator I tried in there was from a junk car, but it was working while still in the car. The second one I tried was a freshly refurbished one from NAPA I know that does not necessarily mean it was good, but what are the odds both were bad?!?!?!

Thank you for the reply, I will try the 2 tests you mentioned next time I am near the tractor. Sadly it is currently 100 miles away so it will not be until next month or so. =)

Thanks again!!

Nick

The alternator output post and the #2 terminal should have battery voltage on them at all times. The #1 terminal is controlled by the switch or what ever other method you have to provide power to excite the alternator. The voltage on this terminal will depend upon which method you used to control the back feed when the alternator is charging. Ideally this voltage should be at least half of battery voltage. If you use a diode in the #1 terminal circuit the voltage should be very close to battery voltage. If you use a light bulb or a resistor the voltage will be less. I do like to see less than about four volts with the switch on. The lower the voltage on the #1 terminal the faster the alternator will have to spin to begin charging. Once the alternator starts to charge there will be charging voltage at the #1 terminal so the alternator will continue to charge even at engine idle.

I had the same thing going on when I converted my H. If you jump around the light or resistor, does it charge? I wound up replacing the light with a push-button switch. Once the engine is running, I hit the button and it charges like crazy.