HCFX2013

Hey all, my brother has a 2007 F150 FX4 5.4L with a fuel gauge problem. It is sporadic, reads all over the place at any given time. It mostly likes to sit in the "way too full" position but sometimes falls below full and sits, then moves again. This issue just started in the last few days. I put the gauge cluster into engineering mode and all of the gauges except the fuel gauge sweeped properly, leading me to believe there's more than a fuel sending issue here.

I'm trying to diagnose whether or not it's a fuel gauge/gauge cluster issue, a wiring issue or a fuel sender issue. I checked out the wiring underneath from the top of the tank to where it enters the cab. In Ford's infinite wisdom they hid electrical connectors behind a plastic cover that is closed at the bottom and open at the top, sitting on the frame rail below the driver's door. It was jam-packed to the brim full of mud, and the connectors have been sitting in it for god knows how long. I didn't have time to test the connections there.

Anybody know what this issue may be to aid my diagnosis? What wires to test?

Mod (Ret.)

Maybe this will help, as it identifies the color codes of the wires that run from the fuel sender (at right) to the fuel gauge (at left).

HCFX2013

Thanks man! Appreciate it. Looks like I'm looking out for an orange and black wire.