Hello, I have been trying to diagnose this problem for almost two strait weeks and can not even put a dent in this issue. So here it is I have 2002 Chevy 2500HD with 135,000 miles on it. The issue is my fuel gauge does not work at all and the PRND321 and the odometer do not work once the truck is on but works fine when I turn the key to the first auxiliary position. I am COMPLETELY lost and kind of at my end. I do not know where to go other than checking fuses

 

What "AMP" is showing when you have the truck in the "ON" position?

 

the first picture is of it in the first auxiliary position and the second one is of the truck running

 

You my friend have a bad Alternator/battery. I would take them both out and go to an Auto store that offers free testing. Get them both tested, and have them test the Alternator at least 3 times to make sure. Mine did that as well and It was the Alternator, You should also double check all the fuses and make sure their isn't any blown. But I'm pretty sure it's the Alternator.

 

Alright I will see what I can do thank you very much !