I just picked up a 1991 Jeep Cherokee Laredo 4wd a couple days ago. It's a 4.0 with 250k on the odo. It had a locked up alternator on it. I have a 1995 Cherokee as a donor and pulled the alternator off of it and put on the 1991. I know the donor alt was good........ I just parked the 95 a couple weeks ago. It's the same alt that came off 91. Now I put alt on the 91 and its not charging at all. Any ideas what could be causing the problem? There isnt much in the way of wires to hook up the alt and its kinda fool proof to mess up as far as hooking them up. My volt gauge is reading notta and the Jeep dies if you pull the positive off of the battery which tells me its not charging. I am at a loss and dont know where to look next. This Jeep has a really good body and the motor runs smooth. It was taken care of for the most part otherwise I wouldnt be messing with it. Any help would be greatly appreciated and thanks in advance.

 

Pulling battery cables off of a running vehicle with a computer controlled regulator is a bad idea. I would measure the battery voltage with it off, start it, then check again. It should be ~12.5 off and 13.5-14.2 running.

 

It kills instantly. I did this only once to see if in fact it was charging. I didnt have a volt meter handy. I was in the driveway of the previous owner with limited tools on hand. I can safely say its not charging though..........

 

Check that the large wire on the alternator is in fact going to the starter relay block on the same post as the hot cable.
You should read 12v there engine off, and 13.7 to 14.1v with it running at the post on the alternator, if so your just not making connection to the battery.

 

Thanks........... I'm gonna borrow a meter and put on it tomorrow. I have had a couple people I know local tell me there could be a problem with the computer. I find that a bit far fetched. I dont see how a locked up pulley would cause that. I was thinking maybe a problem with wires somewhere???? And i didnt know if there was a fuse able link in the mix as well. I'm a novice mechanic and need all the help I can get.LOL