1981 B21F "California" car with air control valve:

Just got done installing the harness I got from Barton. Last step before starting engine was to hook up the negative battery terminal. Huge arc! Can't even hook it up cause it melts holes in the negative battery post. Something is wrong, big time. Please help. I'm going to look things over the best I can, but some help would great.
--
Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 133k

Turns out the fat red cable was grounded to the alternator case. Bad idea. I moved it out a bit so it's not touching the case and all is well. Thanks, Dave, and everyone else. It was a "Duh, now" moment for me.
--
Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 133k

I also have an 81 California 242 B21F. Brown wire from capacitor too. I think its to prevent static in the radio. Which harness was replaced?

More information: I guess sparks are a more accurate description of what I get if I try to hook up the battery. It doesn't really arc through the air, but it's major and burns big holes in the battery post.

I believe I've isolated the problem to the alternator because with the big red cable disconnected at the alternator the shorting out and sparking at the battery doesn't happen. I believe the alternator is hooked up as it should be and as it was. There is a push on female connector(red wire)to the back the alternator. On the positive post are the cable from the starter, and a small brown wire from the a very small black plastic box an the back of the alternator. The alternator is grounded to the block by another separate heavy blue wire. There are three other wires that come off the back of the alternator and go in a harness together to a small metal box behind the headlights.

Any help would be appreciated.
--
Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 133k

I believe I've isolated the problem to the alternator because with the big red cable disconnected at the alternator the shorting out and sparking at the battery doesn't happen. I believe the alternator is hooked up as it should be and as it was. There is a push on female connector(red wire)to the back the alternator. On the positive post are the cable from the starter, and a small brown wire from the a very small black plastic box an the back of the alternator. The alternator is grounded to the block by another separate heavy blue wire. There are three other wires that come off the back of the alternator and go in a harness together to a small metal box behind the headlights.

Doug -

I note that you list two Volvos. I am assuming that the one you worked on is the 1981 242, since you describe an alternator with an external voltage and the 1986 is internal.

I am going to use the 1977-78 the Wiring Diagram Manual, because I think it will be close. There may be some differences though, so double check everything.

There is no brown wire to the alternator. What is shown is (1) the fat red one that carries the charge to the battery via the starter. (2) The thin red wire that hooks to the back of the alternator, (3) a 3-wire harness that goes to the voltage regulater (that metal box behind the RH headlights), and (4) a ground wire that usually connects from under one of tha alternator frame bolts to the rearmost of the bolts holding the bracket on to the block.

That leaves you with a "spare" brown wire, right?

Looking at the various diagrams, I can't see a brown wire at the battery + terminal. There is a smaller red wire that goes to a connection box that is mounted on the same rail as the headlight dimmer relay. (BTW that box lid opens by moving it vertically.)

There is a brown wire that runs from the starter to the ignition coil resistor. If your car has one of those resistors, it will be mounted near the coil. It will have at one end two brown wires, one directly to the coil, the other goes into the harness and turns up connected to the starter at Terminal #16. The other wire from the resistor is blue and runs to ignition control module over by the W/W fluid reservoir.

Check that brown wire and post back, OK?

Good Luck,

Bob
:>)

Yes, this is the 81 with air control valve and throttle switch, a "California car." The brown wire I mentioned comes out of a plastic box about 1 inch by 1 1/2 inches by about 1/2 inch thick that is mounted on the back of the alternator. I think the box is a capacitor. The brown wire comes out of the capacitor and goes to the hot post where the big red wire goes. I'm pretty sure it was always connected there and my son says his 81 is the same. I don't know what's going on at this point.
--
Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 133k

Hi Doug,
Sounds like something at the alternator is grounding the fat red cable. This might be too obvious, but it did happen to me once. Where the fat red cable bolts to the post on the back of the alternator, make certain the terminal is spaced out away from the alternator case. I installed an alternator once where the terminal was touching the alternator case very slightly. It did the same thing with all the sparks.
Dave B.