Fuel gauge grounding location on frame

[NCpogue]

I have an 81 K10 with dual tanks. The fuel gauge reads past full (3 o'clock) on both LH and RH tanks. I installed a new transfer switch (by the way, the effort to switch tanks now is significantly improved over the original factory switch). There appears to be an open circuit and I suspect a ground issue as this would likely be a shared location for both tanks. Where is the fuel gauge system grounded to the chassis ? I see a wire secured on top of the passenger frame rail, between the cab and bed - is this it ?

 

[75gmck25]

On my ‘75 the ground wire comes down through a hole in the frame and is grounded to a screw/bolt on the inside. It’s not on the top of the frame.

 

[Craig 85]

Here's the grounds on my K30. Top of frame.

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[NCpogue]

With the help above, I found the driver side tank ground is indeed routed through a hole in the frame web and grounded on the inside face. Interestingly, the passenger side ground is attached to the top of the chassis. I removed and cleaned both connections but unfortunately the fuel gauge still reads past full for both tanks. As mentioned, I already replaced the transfer switch and the gauge has power because the needle moves when the ignition is turned-on. It seems unlikely that both sending units failed while it was sitting for 7 years, but I suppose it's possible. Is there more low-hanging fruit to check before pulling tanks ?

 

[WP29P4A]

I would use a test lead/jumper and connect one end to the negative battery terminal and connect the other end to the ground location you just found and cleaned. If something changes, you have confirmed a ground issue, if nothing changes, your ground is probably good. A quick and easy test.
A test lead is just a long piece of 18 or 16 gauge wire, preferably with alligator clips on each end to keep it connected while you test. You mentioned checking the ground location near the tanks but you didn't mention verifying the ground makes it back to the battery.

 

[NCpogue]

Ground from battery to frame is good. When ignition is turned on, the needle moves quickly to 3 o'clock. When transfer switch is pressed, the needle stays perfectly still, no fluctuation from LH to RH tank. Guess I'll take a closer look at the ground attachment point behind the gauge.

 

[Raider L]

@Craig 85,
Do you keep gas in both of your tanks all the time? Other than the fact of, "Why have two tanks if you're only going to use one.", what happens to the extra tank if you don't keep some gas in it and switch over from time to time to keep everything open? I have always wanted duel tanks. And the other day when I was out at my local wrecking yard and was getting some wiring parts off of a '76 C10 I noticed it had duel tanks, and man 'o man I started thinking about it again. But with their prices as high as they have gotten I'd be afraid to ask. I might have to rob a bank to come up with the funds.

 

[Craig 85]

@Craig 85,
Do you keep gas in both of your tanks all the time? Other than the fact of, "Why have two tanks if you're only going to use one.", what happens to the extra tank if you don't keep some gas in it and switch over from time to time to keep everything open? I have always wanted duel tanks. And the other day when I was out at my local wrecking yard and was getting some wiring parts off of a '76 C10 I noticed it had duel tanks, and man 'o man I started thinking about it again. But with their prices as high as they have gotten I'd be afraid to ask. I might have to rob a bank to come up with the funds.

Unfortunately, I drive my truck less than 1000 miles per year. I end up just filling one at a time (switching to the other side each fill up). I leave about an 1/8 of a tank in the empty one. Luckily here in TN we have non-ethanal fuel. More expensive, but doesn't break down quickly like regular gas.

Bake in the 90's when I had dual tank squares as daily drivers, I would fill both tanks. Pain in the ass though as you had to set the nozzle down and turn the truck around to fill the other side.

 

[75gmck25]

I also alternate using the two tanks. For example, one is down below 1/4 now, so I’ll go fill it up and then switch to the other tank. I’ll run that one down and then fill it and switch back to the first one.

I don’t drive the truck a lot, so it may take me 1-2 months run one tank near empty, but my switching scheme means I never let the fuel in either tank get more than about 2 months old.

 

[75gmck25]

When you check prices at the yard, make sure they understand that gas tanks are not that expensive. From RockAuto you can get a new Dorman 20 gal fuel tank for about $84, and a new sending unit for $30-$55. Junkyard price should be way lower, since the used sending unit is probably shot.