need help with gas guage, not what you may think...

[mustanglx347]

I bought an '82 Blazer which had been converted from a diesel to a small block. The wiring is pretty butchered. My gas gauge sits on full with the key off, then when the key is turned on, the gauge goes past full into the 3 0'clock position. Well, I did some wire tracing, and found the wires from the sending unit have been cut near the firewall. There is a yellow and orange I think. The black is grounded. I am assuming one wire sends power to the sending unit and the other sends the signal to the gauge (I could be worng). Does anyone know which is which? Also, I need to know which wire on the back of the gauge cluster goes to the fuel gauge.

Oh, BTW, the same thing happens with my oil sending unit. The sending unit has the wire plugged into it on the top, but the gauge pegs out when the key is turned on.

Someone please help...It will be greatly appreciated.

Ben