Reverse lights and gas gauge wont work!

[msullins]

I am having trouble with getting these guys to work. My gas gauge worked one time since i got it (2wks ago) when i filled it up with gas, it registered full that night, but the next day it showed a 1/4 of a tank and has held there ever since... we even replaced the fuel sending unit and tested all the fuses...

As far as my reverse lights, they have never worked since i got the truck, but there is a white half circle switch under my driver side console that will only turn on the reverse lights when put all the way in the left position.. BUT when you do that they stay on even if your in park, drive, neutral, etc.

Can some one please help me with these issues?
It is a 1989 Chevy Silverado with a 305 8 cylinder 5.7L engine.
The engine and Transmission were completely rebuilt.