I have a 1986 Chevy 4x4 w/an automatic transmission and a 6.2L diesel engine. It has dual tanks.

My question is this. Under the truck there is a small ball looking part that has fuel lines going to it ad I don't know what it is. The truck runs without The power and ground wires hooked to it. However when I run power to it it makes a very fast clicking noise. Does anyone know what this part is? I can't find anything online about it and there is nothing in the owners manual that I could find. Thanks for any help.

 

It is probably your fuel tank selector valve.

 

Ah. Ok. Thank you. I have to replace the fuel lines going to it because they are leaking a bit. I guess I will have to trace the wires to the switch. Thanks for the help.