New 91 xj I just put 15 gallons and the gauge is reading quarter tank. After about 3 days of daily commuting on a full tank the light comes on. Previous owner mentioned he recently did the fuel pump I'm guessing he did something wrong. Is there a specific way that the sending unit is supposed to go I haven't pulled it off to inspect it yet.

 

Guessing probably won't work, you'll have to pull the module. If it's an Airtex pump you may want to just toss it and start over.

 

Sounds like resistor on back of gauge....