Volvo 240 charging problem

93Volvo 240 // car will not crank due to dead battery, changed battery and alternator (twice). Alternator charging and cannot not find any electrical draws. Battery has gone dead over night and after immediate use (fast food stop). As info the headlight switch stays in the on position in that the lights turn off with ignition switch. Daughters car away at college. Car in shop for third time…

Verify alternator is charging battery.Carefully inspect the alternator ground wire is(blue wire from alternator to engine block)…also inspect ground cable from batt to engine block/body…check for amp parasitic drain on all positive cables from batt…more than 0.5 milliamps is too excessive and needs further troubleshooting.

I believe this alternator has a “B” circuit. In a B circuit alternator, the field winding (rotor as opposed to the stator) is supplied with a constant ground, while the positive to the field winding is supplied intermittently by the voltage regulator.

In an “A” circuit alternator, there is a constant hot to the field, and the voltage regulator supplies the intermittent ground. This is just some FYI. I hope it helps you. Just make sure the positive field wire is connected to the positive field terminal.
Oh, almost forgot: you may see the word “domain” stamped on the back of the alternator body. “Domain” just means “field”.

Also, I think the only way the alternator body, or housing, or whatever term you wanna use, the only way it gets grounded is by a wire that actually is bolted to the alternator body and then goes to a good ground. (The alternator mountings are rubber bushings, I believe, so the mere mounting of the alternator to its bracket doesn’t really ground the alternator. Tomorrow (WED) I’ll cruise by the Volvo dealer I used to work at and pick their brain for you.

Overcharging can destroy a battery quickly.

Need to know voltage at the battery terminals with engine running, voltage with key off, and most importantly battery electrolyte specific gravity in each of the 6 cells.

There’s a wire harness that comes off the back of the alternator. Then it winds around the engine compartment, where it is subject to oil leaking on it, etc. The insulation can peel off a little and ground out intermittently against the body.

Simplify our info, tactfully send it to the people working on your daughter’s car, and PLEASE get back to us with the final result. I’m always curious to know if any of our info helps out, but people don’t usually post back. Thanks KS