1975 Suburban gas gauge issue, need cluster wiring diagram

[gone huntin]

My gas gauge started slowly going toward empty and finally went way past empty while I was driving it the other day. It has a full tank of gas and I have grounded the wire for the sending unit with no change. I have taken the cluster out and checked all of the wiring and grounds. The weird thing is if you push the needle up and turn the lights on it quickly jumps back to below empty. I have checked all 3 terminals with my power probe and they all show to be grounded with key on or off. I ran another ground from the ground plate under the dash to the cluster with no change. Any help is appreciated. I did a google search for the wiring diagram and got everything except what I need.

 

[diesel4me]

On a truck with one gas tank you should only have one wire going to the sending unit from the ignition switch/dash cluster,its usually a pink or light brown or tan wire,that feeds 12V thru the fuse box,ignition switch,dash gauge,body harness to sending unit....then there is a ground wire from the sending unit to ground at the frame ..

A GM service manual says under "Gas Gauge Always Reads Empty with ignition "on"...":

1. Unplug wire to sending unit...gas gauge should go to full with the key on..

2. If gauge still reads empty :
A. Check fuse..
B. Check for proper connections at dash unit to printed circuit,instrument panel harness to printed circuit.
C. If dash unit is ok,check for opens in printed circuit,or shorts due to pinched wires in the body harness.
D.Remove dash unit and check..

This may be of help also...

Functional Tests of Factory GM Electric Gauges

CHEVYTRUCKS.ORG - Troubleshooting Your Gas Gauge

 

[gone huntin]

Thanks for the reply, I went back and rechecked everything this morning. I was missing the 12v+ to that terminal of the gauge. There was a break in the printed circuit going to it. I fixed that and all is good now.