fuel gauge issue

[Jacksonville1972]

I know this issue has been beat to death on here, but of all the posts I have read I have not seen any where the issue is actually the gauge itself. I have a 1972 C10 that has had a nonworking fuel gauge since I purchased the truck. Since then I have added an aftermarket fuel tank underneath the bed and new sending unit and replaced the fuel gauge resistor. The fuel gauge still does not work. I pulled the brown wire that goes to the sending unit and grounded it. The gauge goes to empty when I open the connection the gauge goes to full, not all the way to 3 o'clock. When hooked up to the sending unit with a full tank of gas the gauge will read 1/4 full. I borrowed a variable resistor and hooked up to the gauge in place of the sending unit, at 90 ohms the gauge reads 1/4 full and goes down from there as resistance decreases, and will go to empty when grounded. Is there something I am missing? At this point I am about to order a new gauge and was just making sure I didn't miss anything before I do.

[M.Lowrie]

Sounds like the gauge and wiring are good, you need to test the sending unit. Remove the sending unit from the tank with the guage wire still connected either touch the body of the sending unit to the frame or run a ground wire to it. Then, actuate the arm of the sending unit with the key on and see if the gauge moves. If it moves, that means that your float on the sending unit may be bad or something inside the tank is restricting the arm to move, like a baffle. If the gauge does not move in the above test, make sure the sending unit and gauge have matching ohm ranges. Most are 0-90 ohm, but I think I've read that some gauges may be 0-30 ohm.
Posted via Mobile Device

[Ol Blue K20]

I think it's the gauge. At 90 ohms should read full if I remember correctly

[JimKshortstep4x4]

As mentioned, at 90 ohms resistance the gauge on the dash should read full.

Before replacing the gauge make sure that the cluster is properly grounded. Although I am sure that the gauge unit can go bad, outside of bad resisters I have yet to see a bad gauge.

I ended up running a separate ground wire to the cluster housing on the last problem because the "clip" on ground wire would not ground the cluster.

Jim

[Ol Blue K20]

Originally Posted by JimKshortstep4x4

As mentioned, at 90 ohms resistance the gauge on the dash should read full.

Before replacing the gauge make sure that the cluster is properly grounded. Although I am sure that the gauge unit can go bad, outside of bad resisters I have yet to see a bad gauge.

I ended up running a separate ground wire to the cluster housing on the last problem because the "clip" on ground wire would not ground the cluster.

Jim

I agree that it could be a ground problem, but you would think with a bad cluster ground dash lights, turn signal indicators etc.. would be at least acting funny if working at all

[Jacksonville1972]

Originally Posted by M.Lowrie

Sounds like the gauge and wiring are good, you need to test the sending unit. Remove the sending unit from the tank with the guage wire still connected either touch the body of the sending unit to the frame or run a ground wire to it. Then, actuate the arm of the sending unit with the key on and see if the gauge moves. If it moves, that means that your float on the sending unit may be bad or something inside the tank is restricting the arm to move, like a baffle. If the gauge does not move in the above test, make sure the sending unit and gauge have matching ohm ranges. Most are 0-90 ohm, but I think I've read that some gauges may be 0-30 ohm.
Posted via Mobile Device

I'm not sure I follow your reasoning. I hooked up a variable resistor, it mimics a sending unit. The gauge does the exact same thing as it was doing with the actual sending unit. If the gauge was good wouldn't it work correctly with the gauge test variable resistor hooked up to it? Not only that the symptoms are the same as when the stock tank and sending unit were in there. I'm having a hard time thinking the stock sending unit the new sending unit and the variable resistor are all giving the same bad readings on a good gauge. I would think it has to be something in the dash wiring, the gauge resistor, which is new, or the gauge itself.

[Jacksonville1972]

Originally Posted by JimKshortstep4x4

As mentioned, at 90 ohms resistance the gauge on the dash should read full.

Before replacing the gauge make sure that the cluster is properly grounded. Although I am sure that the gauge unit can go bad, outside of bad resisters I have yet to see a bad gauge.

I ended up running a separate ground wire to the cluster housing on the last problem because the "clip" on ground wire would not ground the cluster.

Jim

That makes sense to me, more than the sending unit being bad. I'm not sure where the ground on the cluster is. Could you give me a little hint? If not I will figure it out and or run a separate ground.

[Ol Blue K20]

One of the screws on the circuit board make contact at the cluster and just follow that around to the plug to figure out which pin it is. I don't remember which pin it is on the plug off hand.

[Jacksonville1972]

I grounded the dash as mentioned above and it's working. I don't know that I would have ever thought of that on my own. Thanks.