gas gauge not working properly

[secondary-system]

I'm having a problem with my 88 truck the gas gauge isn't wiring properly. when i idle in a parking lot or drive way my gas gauge is working fine but when I'm driving like on the high way the needle flat lines to empty but when i park it in a drive way after driving and let it idle the gauge works again any ideas on what could be the problem?

 

[91'4bee]

The only thing I can think of is the sending unit is bad. Other than that there isn't much that the gas gauge goes off of to my knowledge.

Good luck.

 

[wshiverick]

Not positive but i think you can get to the sending unit from the access panel under the left back seat. Much easier than dropping the gas tank.

 

[KidVermicious]

The fuel pump is under the rear seat hatch, but the sender is not. If it's bad, he'll have to drop the tank.

I don't know how the sender knows if he's idling or driving though. I smell a wiring issue.