I have 1998 jeep cherokee 4x4 4.0L. I've tested the alternater, battery, starter, (they all tested good) and replaced the pick up coil, but the battery is still not charging. It's backfiring, the dash light goes haywire and the speedometer and rev counter lose their readings. I had to run a hot wire from alternater to battery using a toggle switch to be able to drive and keep charge. I have tried to reset the computer by disconnecting the battery, but still have the same issues. It is also burning at least twice as much fuel since the electrical problems have occurred. any suggestions will be appeciated, thanks.
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Disclaimer: I'm no mechanic, but I have been doing lots of Jeep forum research and have fixed quite a few things on mine.
I have a 2001 Sport and had a similar issue: intermittent dim lights, battery not charging all the time, and getting stuck with a dead battery out of nowhere. (Wife not happy.) I looked for shorts, with chafing in the front door & rear hatch harnesses being common, and replaced the battery (was fine).
The problem is simply corrosion in the battery lugs. Chrysler used an arguably too small gauge for the battery & starter wiring harness and corrosion works it's way inside the cables coming out of the battery lugs. The quick answer is to cut off the old lugs, wirebrush the underlying wires to a good shine (making sure to separate the strands), and then putting on new lugs. Even then it's a good idea to shine them again every 6 months to a year, at least I've had to.
A previous owner had already replaced the lugs on mine and everything looked fine. Once I unbolted the wires from the lugs, I could see the corrosion. A 10 minute wire brushing solved all the weird electrical issues. The longer term fix is to replace the battery and starter harness with a larger gauge. There are a few people selling them online (here's one) and they are generally made from welding cable.
I had an issue with these symptoms on my Chrysler minivan. The problem turned out to be a bad battery. It seemed to be ok, but was making intermittent contact because the negative stud was loose, and eventually broke off in my hand. Once I put a new battery in, everything went back to normal and the van has been running great since.