Alternator causing battery drain? Tractor

#1
I know this isn't a tractor forum but I'm not about to sign up on one for a general electrical question.

I know nothing about tractors, i don't even know how to start this old thing. Trying to help the father in law that knows less than me.

Tractor is a '70ish John Deere. Battery goes dead after a few days of sitting.
I measured a .07 amp drain on the battery with everything shut off. I went around the tractor and unhooked electrical components until i saw a change in battery drain. I unhooked the single wire that screws on the back of the alternator and battery drain goes from .07 to zero. Is the alternator bad?
 

luthj

Adventurer
#3
If you still have an alternator repair shop in the area, they may be able to repair the unit for a reasonable cost. Replacing a single diode is usually not difficult. But it depends on the model.
 
#5
I found an alternator pretty easy but the plug is different. There’s A little note with the alternator explain how they have updated the style. Nobody locally seems to have any idea how to get that new plug though, it’s just a Chevy alternator apparently. I have to order it off Amazon.
 
#6
Also I don’t know which wire goes to what. One side of the plug on the new alt is labeled R and the other is F.

Also the new alternator has a ground wire, but the old one doesn't. Tractor doesn't have wiring for it.
 
#10
I replaced the alternator. Battery drain is gone now but it's not charging. I'm not sure it was ever charging. The wire that screws onto the alternator splits and feeds the R terminal at the plugin. Both of these are getting battery voltage at all times. The F terminal is only getting about three volts and only with the key on. Should the F terminal get full battery voltage with the key on?
 
#11
Fixed. Parts store gave me an externally regulated alternator instead of internally regulated.

An alternator for a '78 chevy truck seems to be working now.
 
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