gas gauge stuck on empty

[hatzie]

Originally Posted by 1Cobra427

Hatzie, I was reading your summary of issues and causes. I have the 3rd issue exactly. Left tank on the gauge goes to 3 o'clock and has since I owned the truck no matter if tank is empty or full. My question is the switch you mentioned, it reads correctly for the RT tank. Do I still have a bad switch?

First I would check for a bad tank ground on the RT side.
The tank ground is easy enough to check visually. It runs from the frame to the ring around the sender. Again... This would be the first place I'd look. Remember just because it looks OK doesn't mean there's wire inside the jacket... GM didn't seal the ground lead so it can corrode completely off inside the jacket and look just fine on the outside. I've found forward lighting harness grounds on the radiator support that looked great but were only held in place by the strain relief crimp on the jacket. Run a jumper from a clean spot on the frame to a clean spot on the pinch weld around the tank... Then check to see if the gauge magically begins to work.

Second I'd check the RT side sender wire and make sure it's not unplugged or damaged. The sender wire is fairly easy to follow between the top of the tank and the plug/grommet where it passes through the firewall.

The switch is dead last of the places I'd look. It's easy enough to test if you don't find a problem with the tank ground or sender wire between the tank and the switch.

• Get your meter and set it to measure OHMS or better yet to the continuity buzzer if your meter has one.
• Pull the switch out of the dash and tie a string loosely around the harness behind the plug, so it doesn't escape back into the dash, then unplug the switch.
• The graphic below is a visual of what is happening inside the switch.
• Test from the centre terminal, marked "Out to gauge" in my graphic, to both terminals marked sender in my graphic. One should buzz.
• Flip the switch to the opposite position and test from the centre terminal, marked "Out to gauge" in my graphic, to the terminal that didn't buzz in the last test.
  If the switch buzzes in both of the above tests then it should be OK.

DPDT 5 terminal GM Fuel Tank Switch for 73-80 dual tanks.