02 WJ not starting, electrically related. Trying to start it kills the battery.
 

02 WJ not starting, electrically related. Trying to start it kills the battery instantly. After I try to start it and it seems dead, the gauges kinda, "spazz" and "flicker". I'm thinking it's not actually dead, because what would kill a battery instantly, (besides some sort of short). I'm thinking that these wj's have some weird kind of computer system with some kind of under voltage protection. These new cars are to god damn computerized.
Let me know what you think
Thanks,
Paul

One point. Check your battery cables for good connections. Sometimes the positive (+) cable doesn't make a good connection even though to feels tight. I've posted this so many times, I'm going to go crazy! (more than I am already!)

Is your battery healthy?

With the ignition on, does the battery have enough capacity to operate all the vehicle lights (at full beam). If not, it will not have sufficient charge to crank the engine – and this may be the issue.
Proof of such would be to jump start from a healthy battery.

Otherwise your fault suggests a poor connection within the high current path to the starter motor – most likely at the battery terminals. Check that the terminals are secure and clean.

If you have to disconnect the battery, you will need to enter the radio code, once reconnected.

Lol I know, I post the same thing to so many people over and over again too. I try to to help more than I ask for it, but this is some kind of more complex problem, I've checked all of the basic things, I've got an xj so is understand basic cars. Thanks for the offer I appreciate it, I'm gonna try it

Okay, I'll do it again. The lead cable clamps stretch so that the slot at the clamp bolt disappears, causing the clamp to not tighten anymore on the battery post. You can take the bolt out and cut the slot wider, or replace the cable clamp with a tin plated steel one. I used a Dremel tool to cut the slot wider. If you have any corrosion where the wire is molded into the clamp, replace the clamp.

What's this radio code? Is it some sort of anti-theft device?

99% sure its your battery terminals. My damn WJ would do this crap to me often. Worked on a few other wjs that would do the same thing. It would lose everything as soon as key turns to start but move the terminal cables it will regain power. Mine did this till it ruined the battery

Load test the damn battery first. Any time you have an electrical problem, start at the freaking battery! "Duh, my lights and radio work, so I know the battery is good, duh.." is a bunch of crap! Lights pull less than 20 amps, the radio pulls less if there is no high power amps for your over sized subs. The starter will pull well over 150 amps while you're trying to start the engine, plus the battery is powering the fuel pump, ECM, and ignition at the same time. You're asking a lot from the battery, don't be suprised when they fail. CHECK THE BATTERY FIRST.

It wound up being a grounding problem! I ran a spare starter cable I had from the negative battery post to one of the ac compressors bolts, such a silly thing....

The radio code is just the preset stations, unless you've got an aftermarket unit with theft protection.