PLEASE HELP!!! Charging System Problems!!

I have a 89 Cherokee Limited 4.0l. It is not charging now for some reason. I drove it home and shut if off and came out later to go out and the battery gauge was reading way down. So I checked the stud on the back with the bigger red wire for voltage. It has 12+ volts running or not running which I figured then the alternator is bad. It was only 3 months old. So I have another Cherokee here that I used to drive and took the alternator off it and put it on mine. Still no charging?!?! So then I checked the connector on the side with the YELLOW and BROWN wires. The Yellow has 12+ volts with the key on and none with the key off. The Brown has no voltage. I don't know what those two wires do. Can anyone help me out with this? I've tried everything I can think of.

Thanks alot!

did u try testing ur battey?

I work at a autoparts store and I did check the battery. It's not the greatest battery but it still is ok. The truck is running soley off of the battery, I checked to see if there was a charge out of the alternator and there isn't. I think it has something to do with the yellow or brown wire on the side but I don't know how to check those as I have 12+ Volts to the yellow wire. Thanks for the help so far.

check all the connections and the regulator

OK. I'm thinking though that if I have 12 Volt at the yellow wire and the Red wire then it should charge shouldn't it? The brown wire shouldn't matter. It it does can you tell me how to check it? Does it have something to do with ohms? And one more thing, my voltage gauge is still working. Thnaks

bump, same problem

Hayne's shows a BLK wire going to ground probably from the case (which I recall on mine), is it still there???

It also shows a DK GRN/RED going to the alternator and the igniton coil and fuel injectors and the ECU (same connection....12V?) which means it is probably an alternator voltage regulator output line.

Then a BLK/GRY wire going through a dual 60 amp fuse in the power distribution center (PDC-?-Renix?) and then on to the battery with a RED (12V) wire.

Finally a DK GRN going from the alternator directly to the ECU.

I suspect that if you have the two 12 volt signals at the alternator already (as I recall I had 2 also) and it is not charging, then both alternators are probably bad.

Check at the alternator output screwpost - sounds like either a cooked regulator or you've managed to cook the fusible link going into the start relay screwpost. Checking at the alternator output post will isolate the terminal from battery voltage, if the fusible link is shot.

If you get battery voltage there (no increase, alternator voltage should be rather higher,) then turn the engine off, disconnect the mains cable at the back of the alternator (tie it safely out of the way - it gets battery voltage and will be "hot!") start the engine, and check again. If you're not getting anything out the back of the alternator, you've probably cooked the regulator - it's internal on the Delco units.

I'd have to check the wiring to the regulator, but I seem to recall it's fairly simple, and rarely goes awry...

I used a 1/0 gauge car audio wire and an extra platinum connection to re-ground the motor, and bam... the alternator started charging again. Just a suggestion to try if you haven't, all of my visual, resistance and voltage checks indicated a good ground while my solution proved otherwise. Thanks for the info everyone.

True - checking grounds has become so automatic for me that I just don't think about it anymore...

There are two to really check - the battery to engine ground at the rear passenger side of the block (by the dipstick bracket, behind the distributor) and the engine to firewall ground strap (at the rear of the cylinder head.) Adding a third ground from the battery cathode to the fenderwell sheetmetal isn't a bad idea - I've not done it myself yet, but I plan to. Make sure that sheetmetal is clean of paint and crud under the ring lug for the grounding cables, and that the battery terminals are clean.