need help with gas guage please

[ray_mcavoy]

Chevy trucks used a pink wire for the +12V switched ignition feed to the gauges and a tan wire for the fuel gauge sending unit. Wire colors for your GMC might be different though ... I don't have a GMC specific wiring diagram handy to check.

Here is a good write-up explaining how to test the fuel gauge --> http://6066gmcguy.com/Electrical-02.html

And this paragraph in particular from that site might be helpful to you concerning the connector on the back of the dash:

Check the plug on the back of the gauge panel, check the incoming side at the post lettered "D" & "E". "E" should be power to the dash, "D" is to the sender. Check the printed circuit board on the back of the dash, (GMC Only). Look for brake in the printer on circuits. Repair anything found bad.