Have an 86 Cherokee that I just bought for $300.00 and the fuel gauge does not work. I can't seem to figure it out. The idiot that owned it before me rewired a bunch of stuff and #1. Had the front wipers on the rear wiper switch. #2. Had all the dash lights disconnected. #3. Added a second fuse panel to the center console that has wires going to who knows where? All fuses in both panels are good. #4. Had no power to the turn signals. (Fixed that). Ok so the dash panel is now fully connected and still none of the lights work, fuel gauge don't work (biggest issue), and my oil pressure gauge takes a dive every time I hit the horn. Yes yes I know I bought a project but the motor runs smooth and trans is in great shape. So if anyone on here can help me with this I would be grateful. Thank you all for your time. Pics are up of it. 4" lift on 32s. Have a good day.

 

With "custom wiring" <cough> like that, the best suggestion I have is to remove ALL non-factory wiring, then repair the OEM setup so that everything works. I'm not sure what else to tell you....it's impossible to diagnose wiring problems without seeing the XJ when the wiring is no longer OEM. None of us knows that's there.
Grounds, ignition switch and headlight switch are common trouble spots.

 

pull it all apart and try and trace what wire is supposed to go to the fuel gauge by process of elimination. You might be able to use an ohm meter for this.

I can tell you that the wiring for the fuel gauge goes to a plug that also connects the fuel pump.
This wire will start at the pump and move forward thru a rubber grommet inside the cab under the rear seat. From there it will move under the trim near the drivers side floor into a big strand of wiring and land up under the dash. From the factory anyways...

 

86? What engine?

 

I have zero power going to the plug at the tank

 

It has the 3.8 V6. I know the 4.0 is the way to go but this one runs like new

 

Is that a typo for 2.8? If you really did mean 3.8 that explains why everything has been rewired.

 

Yes typo. My bad. It is a 2.8 I'm not sure why I put that. Must have been thinkin about my old ford courier.