1990 xj fuel gauge works backwards

So i just got a 90 cherokee and i noticed that the fuel gauge is working backwards( when full it shows empty and when empty goes to full) any one ever run into this issue?

is it from Australia?
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maybe sending unit wires got mixed up somewhere down the line?

Or a newer/wrong sending unit was installed.

Johnnie Walker said:

Or a newer/wrong sending unit was installed.

Click to expand...

this

koda279 does your instrument cluster have a low fuel warning indication light? Once a pointer is there you've maybe 3-5 gals. remaining. What'll you do? Drop the tank? Be safe it is gasoline.

Johnnie Walker said:

Or a newer/wrong sending unit was installed.

Click to expand...

blondejoncherokee said:

is it from Australia?
...
maybe sending unit wires got mixed up somewhere down the line?

Click to expand...

The wrong sending unit sounds more plausible.

But the wires at the pump are easy to screw up, the colors change right at the last connector. It has been a long time, but if I'm remembering correctly they change from tan to violet for the sender and from orange to pink for the pump. And some of the replacement pumps have different colors than pink and violet. Even the orange wire changes colors between the connectors front and rear of the drivers side harness where it runs under the sill kick panel and then again where it goes up and behind the side panels. But like I said it sounds like a wiring issue is unlikely, but there are many spots where something could happen to the wiring. I have no idea what would happen if somebody screwed a sill kick panel screw through the harness by accident, but it would likely be bad.

First thing to check is the pump ground. If it is an electrical problem and not a sending unit issue, the first fault point to check is the ground. The second fault point would be the wires, make sure somebody didn't get creative and splice two together or something.

Just had a thought, the fuel gauge is "0" ohms resistance when the tank is empty on the XJ and 80 something ohms when it is full. The YJ is the opposite if I remember correctly.

I meant to say the fuel gauge sender instead of just gauge.

Someone at sometime replaced the sending unit with a newer one, either from a JY or from a part store. I've seen it talked about numerous times on comancheclub while I was building mine. The renix and HO years sending units had different potentiometers in them which if interchanged cause this exact problem.

Mine just moves around seemingly at random. It usually shows E, but it'll bounce around depending on the ambient temperature and who knows what.

Ok, so this seems to be the most current thread I can find on the issue. I just swapped an 88 fuel pump assembly into a 93 cherokee. Surprise, surprise, the gas gauge reads backwards...Now I hate pulling pumps and trying to get them to sit correctly when swapping etc. so i thought up a way that might correct the gauge without removing the pump assembly...

Would it be possible to build a connector/adapter that swapped the 2 fuel pump wires in order to make the gas gauge read correct? Basically cut the connector off of a junkyard/parts jeep, Solder the grounds together, and then flop the other two wires? Does anyone see this as a possibility for working? If it would work, no more need to remove pump assemblies from the tank to fix a bad wire job or a wrong year pump install..