gas gauge
 

ok, so my gas gauge quit working. found that it wasn't getting power from the ignition switch so I fixed that. the gauge went right to full. I thought that was odd, so I pumped out about 5 gal of fuel. gauge still showed full. traced the wires from the dash to the tank in the rear as far as I could get. any ideas what to check with out dropping the tank. its in the rear and a pain to get to the sending unit.

Re: gas gauge
 

The tank reading full all the time indicates some sort of high resistance somewhere - a classic ground problem

Run a dedicated ground from one of the mounting tabs on the gauge to a known good ground point under the dash. The back of the dash usually has some paint on it that makes grounding a problem. I'd clean the gauge mounting pads with some sandpaper or Scotchbrite too. You could even use the battery negative terminal for a test.

Next, run a dedicated ground from the sender at the tank to a known good chassis ground too. Tanks are often mounted with rubber under the straps and this can cause issues.

Re: gas gauge
 

our truck fuel gauges are pretty basic

https://67-72chevytrucks.com/vboard/...9&d=1380781258

Re: gas gauge
 

I'd say along with doing what E015475 (that took three check backs to get right) said but add when you have the sender out check it with an ohm meter.

I'm thinking that the gauge should go from 0 to 30 ohms. If the meter moves right with the sender the sender should be good and you figure out what is causing the high resistance.
Corroded wire ends on a ground wire or a ground wire that isn't making good contact would be the first thing to look at. I'm not sure how these tanks grounded from the factory They may be grounded through the straps and contact with the body.

If you haven't taken anything apart yet you might try using a good jumper wire from the sender body to a good clean ground. Or make up a ground wire and run from clean bare metal under one of the screws of the sender to a clean bare ground. That probably should be step one if you haven't already done it. Then if that doesn't work pull the sender out and start testing.

Re: gas gauge
 

"Corroded wire ends on a ground wire or a ground wire that isn't making good contact would be the first thing to look at."

Bought a rebuilt gauge from Jim Carter along with a new tank sender a couple years back.

Just got the truck running last month, and the fuel gauge wasn't working. Had 12V at the terminal. Dash lights worked so I assumed my ground was ok.

Checked the wire from the sender underneath the dash to a good ground - perfect.

Packed the gauge up and returned it to Jim Carter to replace the fuel gauge. They called me and said there's nothing wrong with the gauge and "did you make sure the case of the gauge was well grounded?". Indignantly i said "Yes"

Got the gauge back today. Just for fun, I checked the resistance of the sender to the mounting post for the gauge. It read 200 ohms. When I measured the sender's resistance to ground at the battery negative cable, it read 15 ohms. (and that's correct for about a half a tank of gas, which I think is what's in there) Bad ground.

I think Jim Carter Truck Parts is right - the gauge is fine and the faulty ground is the problem. Maybe yours too.