i have a 2002 ram 2500 diesel fuel gauge reads all over the place any suggestions where to start

 

Check the wiring from the sender for chafing.
If you don't find a damaged wire you may need to install a new sender. (Sometimes the pivot for the float gets worn and causes intermittent breaks in the circuit, making the gauge drop to zero and come back up again. Sometimes the pivot sticks and lets the gauge read higher than what is really left)

 

I was thinking a wire sometimes stays on full sometimes empty and sometimes I think it actually is working

 

Sounds like the sender to me.. They can be bought at geno's garage and some other places for a lot less than at the dealer..