1991 Volvo Alternator Won't Charge Battery

240bri · Post by **240bri** » 01 Oct 2014, 11:49

About two months ago my 91 240 wouldn't start, so I jumped it but wouldn't hold a charge. I checked my Bentley manual, which says that the battery warning light (wired in series between the small positive alternator terminal (D+) and the battery) needs to work for the alternator to operate. Warning light is fine, so I get a rebuilt alternator that was missing the pulley and there was no bolt on the grounding terminal, probably because the threads were a little messed up. Seemed like signs of a careless rebuild, but I installed it anyway. Still not charging. Check alternator ground, OK. Check voltage at large positive terminal (B+), present. Check voltage at small positive terminal (D+), nothing when car running or off. Assumed it was a bad rebuild, and exchanged it for another rebuild. Same problem, no voltage at D+. Check for shorts between positive and ground, find none. Now battery warning light is not working. Check bulb, OK. Afraid that bad rebuild may have damaged something. Seemed unlikely to get two bad rebuilds, but possible. I got fed up and installed a GM 1 wire alternator, which worked fine (though I lost all my gauges, something I'm used to haha) until last night when the belt snapped because I could never tension it properly. I'd like to fix this correctly, but I'm at the limits of my knowledge, and I'd appreciate any advice, thanks!

93Regina · Post by **93Regina** » 01 Oct 2014, 19:50

240bri wrote:Check voltage at small positive terminal (D+), nothing when car running or off.

Well now, if that's the terminal where warning light hooks to...then put a positive voltage there

240bri · Post by **240bri** » 08 Oct 2014, 17:45

Thanks Regina, sorry for the slow reply, I didn't think my post went through. I'm new here haha. I was in the process of trying that when a new problem popped up. Now I have a short circuit to ground. I reinstalled the stock alternator, and while I was doing this I disconnected the air intake to get at the bolts on the compressor to put in new alternator belts. I also had the grey wiring harness on the firewall undone. Those are the only wires I remember touching. I disconnected the alternator completely and still a dead short. I pulled out all the fuses and put them back in 1 by 1. Fuse #8 (powers radio, central locking, clock, interior lights) gives a dead short to ground.
Fuse #9 (hazard lights) and fuse #6 (fuel pump and fuel injectors) each read about 20,000 ohms to ground. I'm not sure if these fuses are shorting out through a relay (giving the high resistance), and I'm afraid if I power up the car, the relay could open and give a dead short.

I think I must have pulled a wire loose, but I haven't been able to trace it. I can't find any wires with bare insulation or anything touching the chassis that shouldn't. I can't visually find the short....

93Regina · Post by **93Regina** » 08 Oct 2014, 19:56

240bri wrote:Now I have a short circuit to ground....I can't visually find the short....

Use a Non Contact Temperature Measurement Gun

240bri · Post by **240bri** » 09 Oct 2014, 03:23

Wouldn't I have to hook the battery up to use a temperature gun? The short happened with the battery disconnected, and I'd rather not risk damaging the wires and components by letting any fault current flow. That's why I've been using an ohmmeter to trace the short.

93Regina · Post by **93Regina** » 09 Oct 2014, 05:43

240bri wrote:The short happened with the battery disconnected...

Good Luck!

One to Remember · Post by **One to Remember** » 09 Oct 2014, 06:52

First off put the right alternater on it. I don't think GM makes Volvo but even then get the right one. Run the positive to the battery but have a toggle switch in between that line and have access to the toggle or home light switch or whatever you use under your steering column so you can hit it on start up. If alternator needs better ground ground it to the frame with some good wires as a redundant ground. That is how we will directly bypass things. By a new relay or use the above method or bypass the relay using a simple wire where the relay's connectors plugged in.

240bri · Post by **240bri** » 11 Oct 2014, 20:53

It turns out there was no short circuit, the resistances I was reading were just the loads of the different relays and devices. I hooked everything back up and no fuses blew. I jumpered from b+ to d+ with an in line toggle switch and 5A fuse and now the brick is back.

240bri · Post by **240bri** » 11 Oct 2014, 20:53

It turns out there was no short circuit, the resistances I was reading were just the loads of the different relays and devices. I hooked everything back up and no fuses blew. I jumpered from b+ to d+ with an in line toggle switch and 5A fuse and now the brick is back.