80 K10 Fuel Gauge

[A-B Slinger]

1980 K10

Dual tanks. Yesterday when I started the truck the fuel gauge read slightly over 1/4 tank although I knew both tanks were full. LH or RH it reads the same. Took the truck out of town running on the LH tank and the gauge for the LH reads 1/8 after 100 miles and the RH 1/4. Refilled and LH again reads 1/4. Tried running on the RH tank and get the same readings after approx. 100 miles as I did with the LH tank. All wiring seems to be connected and in order. Any ideas ?

Thanks ahead

[chengny]

Just as info - if it hasn't been updated/modified your tank switching system is the single wire type. This system changes tank suction by use of a solenoid - hence the "single wire".

There are actually 2 other wires that run from the dash switch. One each for level sensing in the production and auxiliary tanks.

The power on/off to the solenoid (no power defaults to the production tank and power on moves and holds the solenoid valve in the auxiliary tank position) and change over of level sensing is accomplished within the dash mounted switch.

Wiring diagram if you are interested:




Anyway, since the sudden loss of level indication is occurring in both tanks, that would seem to point to a power or ground issue with the gauge itself. If it were only happening to one of the tanks, the problem would most likely be in the wiring between the dash and the tanks. But it's not , it's common to both sides.

Refer to the dwg and find that tan wire that leads from the gauge to the control switch. Disco it from either the harness plug or the control switch and jumper it to a good clean ground.

When the sensing leg (the tan wire) is connected straight to ground, the dash gauge should peg high. If it doesn't check the harness connection at the back of the instrument panel PC board, the main ground wire at the common bus. I am not sure were that is on a 1980, but if it's like the later models it should be on the inner fender wall above the parking brake assembly.

If neither of those steps help, it is probably a failing gauge or circuit board.

[A-B Slinger]

Your help is greatly appreciated.

[motornut]

"When the sensing leg (the tan wire) is connected straight to ground, the dash gauge should peg high. If it doesn't check the harness connection at the back of the instrument panel PC board, the main ground wire at the common bus"

actually it should go to empty,loose or open it will go over the Full (3oclock)

[rich weyand]

When the gauge reads 1/4 on a full gauge, and is proportional down from there, it is usually a bad balance resistor on the back of the gauge. This happened to me, I replaced the resistor (which is a PITA because everything has to come out all the way back to the gauge in order to remove the gauge and replace the resistor), and has worked fine since.

This is the source for the part I used:
https://www.classicmuscle.com/p-6237...-resistor.aspx