[joel_md]

My 1971 John Deere 120 has an electrical problem causing it to not charge. Many years ago I had a similar problem and I remember the voltage regulator had a fuse that would occasionally blow. However, I had to replace the regulator a few years ago, and the new one doesn't seem to have a fuse. Anybody have an idea where I should start to diagnose the problem?

Joel

 

[ereed011]

Joel. There are a few things you can check. You will need a volt/ohm meter that has AC volts on it. The digital ones do not work as well. I need to use the analog one to check the stator out. This would be the meter with the needle on the face.
First you have to unplug the stator wires from the regulator. Start the tractor and at a high rpm plug a lead into each of the wires coming from the stator. Meter should be set on AC volts. You should get 28 to 30 AC volts. If you dont , the stator is bad. If you do the regulator is bad.Its that simple.
This is assuming that all the wiring is good, and the battery is good.
The wire you want to check is the one coming from the regulator to the key switch. Make sure that carries current .
The other problem could be the key switch itself. It could have bad connections or the switch inside has bad contacts.
If stator checks out , you can put the meter across the battery terminals to check if it is charging at about 14 volts.
The meter should be in the DC volt scale.
Check these items out first .
Let us know what you get for readings.
Roy

 

[joel_md]

Roy, thanks for the help. First I cleaned the battery terminals and other wiring connectors to remove corrosion. I could not find my Fluke meter, so I borrowed a neighbor's voltmeter. Unfortunately it was DC only, so I could not check the stator voltage. I put the contacts across the batt terminals with the engine idling, at high RPM, and high RPM with the PTO engaged. It always shows 12.5-13.0 volts. Apparently it is charging, but not at the proper voltage. I'm thinking maybe the battery is the culprit here. When I put an automatic batt charger on it, the gauge indicates it never gets fully charged.

 

[vinnie110]

You could take the battery to a local auto parts store or WallMart and have it tested. Make sure the body if the regulator is properly grounded.

 

[ereed011]

It sounds that way. Do you have another you can try in there ?
Roy