Ok so here is my issue, I have a 1967 C10 body on an 81 Chevy 1 ton frame. I am in the process of restoring the truck and replaced the dash cluster I also replaced the fuel tank and sending unit. The fuel gauge is for a 1967 C10, the fuel tank and sending unit is for a 1981 suburban. The tank is 40 gal, but when my tank is at 20 gal(half full) my gauge reads full. What could I do to fix this, or what should I do?
gm did not change the OHM resistance values between the 67 and 81...so stick the 81, 40 gallon sending unit back in...if you look at the two of them side by side...you will note that the arm on the 40 gallon version is mounted at a different position.. so when the tank is full.. the float lever is near the top of the tank...and when the tank is empty.. the float lever is just above the bottom of the tank..with the sending unit that might have been from the behind the seat tank..the depth might be similar.. i could not find that the position of the resistor is just in the wrong place..if you have the original sending unit.. compare the 2 with a digital volt meter set at 200 ohm scale.. and then note the height of the float on the arm with it up and with it down.. i have not compared to see if they fit at the same angle..there are several brands of new sending units for the 81.. becareful.there if you use some kind of jumper cable to ground the sending unit to the frame.. you can lift the float to the top and then let it move down.. and see if your gauge follows...
I purchased both from lmc trucks and never had the original tank for the 67 or the sending unit. It had a 20 gal fuel cell mounted on the truck which was not even wired to a gauge. but i will see if I can find out what is going on.
Unplug wire off the sender and ground it while watching the gauge (with key on, of course) gauge should swing one way or the other. If it does wiring etc should be ok.