Have a 99 3/4 ton gas engine..... Had 3/4 tank of fuel - get in the truck & the gauge was swinging wildly to E with the amber low fuel indicator on & then would swing to F -- just going back & forth. Then it just stayed on Full. So I ran the gas tank low & replaced the fuel pump / sending unit assy with OEM part & now I'm back to the wild swinging fuel gauge again. I am flamboozled by this. Looking for a wiring diagram & any ideas. almost seems like a bad ground or something. Can anyone chime in on this?

 

Download the 98 service manual from here. Wiring diagrams are in section 8w.

Can also do a cluster test.... Just hold in the trip reset button, while turning the ignition to On. (not start) Should sweep all the gauges, blink all the lights, etc.

 

we've done the cluster test and gauge acts normal. hoping the wiring diagram helps. thinking we have a flaky wire. can't believe the new oem pump / sender assy is bad.


the overhead trip computer is all over the map too. Says "SC"on it also

 

No idea what that means..... should be in the service manual as well.