Fuel gauge not working properly

Good morning,

I attached a wiring diagram of the system for you. You need to go to the switching valve under the truck on the frame rail and test the yellow wire for voltage with a voltmeter. It should have about 7 volts on that line for the sender units.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

If it does not have power, then go to the dash and check the yellow wire at the dash for power. If it has power, you have a wiring issue. If it does not then the cluster is the issue.

Roy