Fuel Gauge (again)...need instructions on checking ohms

[Jeepwm69]

I did a search here, and from other posts it looks like my gauge might be bad.
Gas Gauge didn't work for years (read way over full). I dropped the tank, found the pink wire was severed. I spliced it back together, and everything's worked fine for a few months. The other day I looked down and it was just a hair under full (which was correct). Looked down a few min later and it was on 1/4 tank. Looks like 1/4 tank is where it goes for a bad ground on the tank or a bad gauge. Given that I have to drop the tank or remove the bed to mess with the sending unit wires, I'd like to check and see if I'm getting the proper signals at the guage first.
To check and see if the wires are sending the proper signal, I take my trusty voltmeter, put it on ???? setting, and then put the black post on the black connection on the gauge, and the red post on the pink post on the gauge, and then given that I have just a hair under full on the tank, I should read somewhere close to 90 ohms, correct? Do all this with the key off?

I really, really hope I don't have to drop the tank again. That was a major pain.

[Goldfinger]

Gauge could have been sticking or lost power. If it was a short it would read at 3 o'clock.

[hatzie]

Bad Ground pegs the gauge at roughly 3:00
Dead shorted sender will read E.
A mildly shorted sender wire could read anything.

You can test the sender in the dash.
Remove the fuel gauge because the movement coils and calibration resistor will affect your meter readings. Leave the housing in the dash.

Set your meter to the 100 ohms scale.

There are three spring tangs arranged in an upside down triangle in the fuel gauge pod.
Fuel Sender on the right. The point of the triangle is GND and it faces down. Full should be roughly 80-90ohms from sender to ground.

This is the printed circuit image from the 1979 GM wiring diagrams for a visual. NOTE the view is looking at the back of the cluster and upside down...

[hatzie]

You can test any of the gauges but the tach and ammeter with a 12v battery.
A working gauge will read past the top (H, F, 60, ...) when you hook +12 to IGN & - to GND
It will bottom ( E, C, 100, ... ) when you move the ground to the Sender pole.

If the needle moves both directions but doesn't reach full sweep may be able to repair your gauge. There are sender specific calibration resistors on the back of each of the gauge cans in the cluster pod. They sometimes corrode or loose contact.

[Jeepwm69]

Thank you for the reply. It will probably be first of next week before I get to it, but I will post up what I find.

[Nothinghead]

What did you find? I am looking into a repair of my fuel gauge system as well.