Hello,

I just bought a 1987 F150 last week. It has an issue with the fuel gauge that I can't figure out in my head, so not sure where to start with troubleshooting. Im hoping you guys can help me out!

The fuel gauge on both tanks show empty when the truck is running; however, they show accurate readings when I just have the key turned on in accessory mode.

Could it be a faulty ground somewhere? If so, where should i start hunting it down? The other piece of info is that the previous owner told me that he swapped out the ECU in the past...hopefully that is not the culprit!

Thanks in advance

 

Start with the wiring for the dash selector switch.