So I got an oil change and the monkeys there busted off the field wire to the alternator. So now the battery doesn't charge. Simple fix, right? Just reattach the wire. Well, no, that didn't work. I'm reading about 8 volts from the negative battery terminal to the binding post on the alternator. The B+ cable is fine; 12 volts to ground, same as the battery. Sometimes it works to run a jumper wire from the positive battery terminal to the post on the alternator; it spins up and starts putting out 14 volts. But lately it doesn't. Any thoughts? I am thinking maybe it's a bad voltage regulator.... ? I actually have a spare alternator I can put on, but I don't want to kill that one by installing it into a bad electrical system. Any light someone can shed on this would be appreciated.

 

You didn't say what yr or model.

On my 740 its simple to pull the regulator and brushes to check for wear.
i installed the internal adjustable regulator with brushes from Barton's.
http://davebarton.com/AdjustableVoltage.html

 

Oops sorry. It's a 1989 240 wagon. I'll examine the regulator; does it sound like that might be the problem?

Thanks,

Sam

 

I've read the voltage usually goes high when the regulator dies, low voltage sounds like brushes.
2 screws and they're out.