Was working on my rear brakes last weekend and had the rear wiring harness (fuel pump, transfercase, and transmission) hanging down. After I fixed my problem with the rear brakes, I took it for a quick spin out in the back yard to check out the brakes. Not thinking to well I left the wiring harness hanging down and the wire wrapped around the rear driveshaft and the Jeep died.

The fuel gauge wire was the only broken wire and spliced it back together. The Jeep still would not even turn over. Checked all the fuses but none were blown.

Then I discovered that the pin pulled out of the connector on the main wiring harness. This connector plugs into the rear wiring harness that goes to the fuel pump, transfer case, and transmission. I pushed the pin back in and the Jeep cranked over but it still will not start. I used starter fluid and the Jeep started up and died pretty quickly. This leads me to believe that the fuel pump is not working. I also noticed that my fuel gauge inside the Jeep read full and before I wrapped the wire around the driveshaft it read ¼ of a tank.

So I believe that there is a problem with the three wires that connect to the gas tank sending unit. I looked up the three wires for the fuel pump in my manual. 1st wire is ground, 2nd is 12v from the fuel pump relay, and the third is the fuel gauge. The ground and 12v lines did not measure any voltage. I then measured the resistance of the ground wire to metal on my Jeep and is showed it was open. The fuel gauge wire measured 6-7 volts. It was getting dark so I called it a night. I am not sure if I had a good ground to measure the resistance of the ground wire so I am not 100% sure it is a floating ground.

I think two of the wires are still bad or just the ground wire is bad and the fuel relay uses this ground wire to work and that is why I am not measuring any voltage on the 12v line for the fuel pump.

Question:

1. Once the Jeep key is turned to the on position, should the fuel pumps 12 volt line be hot (12 volts) all the time?

2. The fuel gauge reads full and I measure 7 volts on the fuel gauge wire. I know the tank is only 1/4 full but after my Jeep died it reads full. Since I read 7 volts on the fuel gauge wire this leads me to believe that the ground is bad at the fuel pump and not completing the circuit. Is this what you would believe also?

3. If the ground is bad on the wires to the fuel pump will the fuel relay still work? I noticed that the starter relay gets its ground from this wiring harness also and it did not work until I fixed that ground.

 

WTF - go join a Jeep forum.

 

nah, should have constant 12 all the time. well im sorry for the first 3 seconds. then when u turn it all the way on (start it) it should have constant power. sounds like u need a feul pump and usually the gauge comes attacht as a whole assembly inside the tank... thats just my - good luck

 

dumb question ...but why would u have the transmission out to do brakes????......but also check fusible links sometimes those go to ...

 

transmission was not out. The electrical wiring runs right along the brake lines. I unclipped the wire and let it hang down as I worked on replacing differnt parts of my brakes.

I replaced the front brakes with GM 1 ton brakes and the rear brakes went from drum to cadi el dorado disk. Also changed the master cylinder to a 1968 corvette. The stock jeep brakes could no longer stop my over size tires. Now they work mint.


Choose you can not replace the fuel pump yet. There is no 12v going to it so of course it would not work. I was just wonderign about the three wires and how the fuel pump worked. I am off Friday so it should be fixed by then but if someone has some ideas I rather spend 30 minutes fixing it then all day trying to troubleshoot.

Remember all was working before I wrapped it around my rear drive shaft.

 

sounds to me like you have a bad ground!! I can't imagine that jeep having wiring issues. Dude sell that heap and buy a real vehicle.