Alternator won't charge battery 86 240
 

I bought an 86 240 that had been sitting for years a while back and have slowly been fixing a whole host of issues, and when I finally got it running the battery wouldn't hold a charge. I bought a new battery, alternator, and positive battery terminal lead, but nothing solved the issue. Then I noticed that the smaller red wire attached to the alternator was frayed near the end. I cut off the frayed part and put a new connector on hoping that would solve the problem, but it did not. I still think that might be my problem though, because I read on another thread that if the small red wire was connected properly then all of the lights on the dash should come on when the key is in the on position, but when I turn the key to the on position the only lights that come on are the oil, battery, parking brake, and brake failure lights. Do you think I'm right in assuming that the wire is probably damaged further on somewhere? It drops down under the engine block somewhere so there's no way I can trace it back all the way. My only other ideas are that I either bought a bad alternator or I may have connected the positive lead for the battery incorrectly (it has a small wire that connects to a junction box on the drivers side of the engine bay and I wasn't exactly sure which connector I pulled it off of originally, but they all seemed to be part of the same connection so I'm not really sure if that matters). I was pretty close to calling up a junk yard to haul her away these past few weeks, but I've already put more time and money into this thing than any sane person would and really don't want to give up.
https://cimg8.ibsrv.net/gimg/volvofo...3ff70a2031.jpg
Any thoughts are much appreciated. Thanks!

I just rewired the skinny red wire that goes from the alternator to dash and the battery still dies(although I left a little bit of the old wire that was attached to the dash). I guess I'll just rewire the entire alternator and see what happens. Does anyone know if it matters which one of the wires that goes to the starter is on top (alternator or battery). Doesn't seem like it would make a difference to me, but when it comes to electrics I'm pretty dumb.

when you start the car does the alternator light(battery) go out ?

when you turn on the ignition, do you measure some voltage at the skinny wire D+ terminal on the alternator ?>

when the engine is running, do you measure 13.6-14.2 volts at the big B+ tterminal ?

last time I had alternator charging problems, it turned out the alternator ground wire wasn't any good. I could measure voltage from the alternator body to the battery - lead, which normally should be very close to 0V difference.

Pierce gave you some good advice. I would only add that your "86 is right in the middle of the "deteriorating insulation " of the main wiring harness model years. That thick red cable runs from the alternator to the area under the crankshaft pulley/timing cover area on it's way to the battery. That's a common place for the insulation to break down and contact the block, thereby grounding it.

Yes, the lights go off when the car is started. Here's what I found over the past couple days: the ground wire for the alternator was in pretty bad shape, so I went ahead and replaced it. The alternator belts were also pretty slack, and I couldn't get them any tighter, so I swapped those out. I went ahead and pulled the positive wire out and checked it as well while I was down there and it seemed like it was in pretty good shape. The connector for the oil pressure sender was also completely corroded, so I'm gonna have to figure out how to keep a bullet connector from falling off of it because I can't seem to find an aftermarket connector anywhere. I also saw on another thread that someone just ran a direct line from the positive terminal of the alternator to the positive terminal of the battery, so I'm probably going to do that as well when I start putting everything back together because I figure it can't hurt. I'll let you know what happens when I start her back up.

search for "Oil Pressure Sensor" on this page, https://www.240turbo.com/blackvinyl.html and buy the 'standard' 1mm wire pigtail version with the closest color to the original (I think its black). use a marine grade sealed heatshrink crimp splice to join this to the existing wire, like these, (should be able to find these in much smaller qty at any marine/boating store, and maybe at a decent auto parts store). 1.0mm^2 wire is between 16 and 18 AWG, so I'm not sure if the red or blue crimps are more appropriate. alternately, use shrink wrap and solder the wire, but old automotive harness wire can be hard to get a good solder flow.

So I've got the alternator hooked back up and the battery is holding a charge. I think the main problem was poor tension on the belts, and the ground wire may have also contributed. Now I just have to connect the oil pressure sender and we're ready to roll! Thanks for the input!