First off, I have a 1999 Jeep Xj 4.0L. The problem I am having has only happened twice within a week span. About a week ago, the jeep barely started, the radio reset, and I had to hold my foot on the gas, for about ten minutes to it idling on its own. It seemed like a dead battery, but the battery gauge was where it normally is, and its a marine battery so it has a green/ red-eye, the green is showing meaning that the battery is good. This brings me to today, (the jeep ran fine all of last week) I get in it this morning, the solenoid clicks and the radio is reset again, but the jeep won't start. I bought a new starter, I decided to eliminate the possibilities, and it seemed that that would be the issue. So I put a new starter in it today, and go to start it, the solenoid clicks, and the jeep loses all power, the door lights won't work. The only things that work are what I hard wired to the battery. I checked relays, fuses, and the grounding and power wires and they all seem to have good connections. This is my daily driver so I need some guidance, thanks in advance!

 

I think you need to recheck those battery cables. It sounds like a classic connection problem. Cables can be corroded inside the jacket, so you need to get rough with the connections and cables. Pull, push, tug, yank. If it's bad, you want to break it, so that you know it's bad. Then you know what to fix.

Also, you cannot be sure of the state of a connection by looking at it. You need to take them apart.

Don't rule out a battery problem. If there is a bad connection inside the battery, your green light will not show that.

 

X2 on 20-yr old rotten battery cables and corroded connections. Don't forget to look at the ground cables, especially where they connect to the block and the firewall. If you have a voltmeter, check the battery voltage without it running to get an idea of how charged it is. Sounds like the alternator is fine if the voltage looks okay running. Most auto parts places will load test the battery for you.

 

I tried everything I could, I thought about the battery, but then I tried to jump it, because even if it’s junk, a jump should still start it. But it did not. Checked the cables, the positive are a little iffy but I replaced the negative cables and nothing. I took it to a friends who owns a shop and we’ll see if we can try and fix it tomorrow

 

Sounds like a bad ground or loose battery connection. You'll have to be a bit more descriptive. Is it cranking and not starting? or no crank, no start?