I did some diagnostics on my aux fuel tank because the gauge pegs to super full every time I use it and stays there. I assumed it was either a short somewhere in the wiring or a bad sending unit. I removed the fuse and it stayed pegged. Does this mean there's still a short upstream from the fuse block for the aux unit? Am I off track? Also, I have no dash or heater illumination at night. I have a new headlight switch, all the bulbs work and there isn't any corrosion on the contacts. Thoughts? Thanks for any advice anyone can offer.

 

The fuel gauge is not protected by a fuse on these trucks. The fuel gauge is powered from the instrument cluster voltage regulator (ICVR), which is powered directly through an 8.5-ohm resistor wire. This is hot anytime the key is on. The fuse you're looking at on the fuse panel is for the solenoid, not the gauge. This is why removing fuses does nothing - the circuit doesn't even pass through the fuse panel.

If the fuel gauge pegs to full regardless of fuel level, then there is a short to ground downstream of the fuel gauge. It could be in the dash itself, or anywhere along the frame. The sending unit could also be bad (shorted rheostat).

If your dash lights are gone, check for power at both sides of the fuse. If you only have power at one side and not both, replace the fuse. If you don't have power at either side, then the problem is upstream at the headlight switch. The new switch could be bad, or the dimmer could be turned all the way down.

Alternatively, if the other dash lights are coming on (headlight/wiper switch illumination, and gear selector indicator for A/T), then the problem is isolated to the instrument cluster and heater control panel.

 

Thanks for the quick response...I'll keep searching for the short in the aux fuel wiring/sending unit. I have no lights at all anywhere at night. I'll check the fuse on both sides. The old switch did the same thing this new switch does (installed it today). The rheostat seemed clean on the original unit at least, but who knows. I think it has the original printed curcuit, and it's starting to get brittle.