At the back of the alterator '86 740 there are to + connections B+ and D+ What is D+ do? Is it for the Dash Ammeter? My car has nothing hooked up to this D+ terminal
and since my alternator is not working, I'm kinda wondering. I used a voltmeter to
measure the voltage at the B+ alt. terminal while the car was running and it read 11.43 volts with no difference when revving the engine. I get 11.43V at the B+ but less than .02 volts at the D+. I just installed a new ground wire so I rule that out. I did drop a wrench which caused some sparks in the alternator area durng a recent repair. Could this have fried the Reg/diodes etc? All my problems started after the sparks flew. My car wouldn't start after some repairs in which I was using a light hooked up to the battery for a few hours. When I jumped it it wouldn't stay running. I got it charged and it ran down again. I pulled the Alt. and had it tested at AZone. They said it was ok. But obviosly it is not. the brushes look ok. I am thinking of heading to the Junkyard and pullin a few Reg/Brush assys, and trying that. Other than that what could it be?

Having a bad day,
740man '86 740

You should have 2 wires on the alternator, (not counting the ground wire).
The heavy gauge red wire to B+ and the warning light wire which goes to D+.
The warning light supplies the excitation current to get the alternator charging.

No light = No charge.

You should have a light gauge wire emerging from the loom at the same point as the wire for the oil pressure warning light (just checked on mine, it`s red) if you ground this wire with the ignition switched on, the charge warning light should come on, as well as a load of other lights.
If you want to check the alternator, connect a 5W bulb or test lamp across B+ and D+ to simulate the warning light.
I think you have knocked the wire off the D+ plus terminal and it is now lurking behind or below the alternator where you can`t see it.
Find that wire and refit it, or run a new one and I`m sure all will be well.
Good luck,
Colin.

Colin,
Thanks a million! I rigged the test light and it finally worked! I have a pretty ragged harness and that D+ female connector is missing. I've noticed it on other Volvos and on the replacement harness the I am going to put on. I thought since there was none on mine and my car ran fine that it was for an ammeter or something and wasn't needed. I thought it was unusual that the previous owner had run TWO ground wires off of the alternator, one from that D+ post. It was obviously grounding the D+ connector allowing the alternator to charge. When I removed the Alt. to have it tested, I replaced it with a proper ground wire, leaving the extra one off and there is where my troubles began. I think it is time to put on that new harness, but for now would a resistor between the two terminals work?

Thanks again,

740man Phoenix, AZ USA

Glad you have it sorted.
Yes,you could put in the equivalent value resistor to your lamp but personnaly I would just make the lamp a more of a permanent fixture and you would still have an indication of alternator function.
Alternatively, if you just strip the loom back a bit you should find the existing wire to which you can splice a length of wire and have the light in
the car work again.
Colin.

If i was you at this point in time i would just replace the voltage reg to rule it out, its possible that you shorted it out, if you didnt remove the alt or move any of the wires ad it still doesnt work its a high possibility, additionaly if you had the key in the on position when this happened id check all your fuses, also you will want to check the + wires to and from the alternator to make sure you didnt frey any of them.