81 c-10 pickup 350 5.7L oldsmobile diesel starting system info needed

on an 81 c-10 pickup with the oldsmobile 5.7L diesel engine and auto transmission i need to find out possible reasons why the ignition switch will not send power to the starter solenoid,

in order to crank the engine you have to hot one of the little wires at the white plastic rectangle electrical component thats right byt he ford style starter solenoid thats on the driver side fender wheel tub,

i need ot find out where i can find out about this system, or who would know or anything online like a schematic, etc.

i assume that the electrical ignition switch on the lower part of the column or the rod down to it from the key ignition lock switch is at fault, but does anyone know what else it might be and also how to know if its the electrical switch or rod other than by havint ot drop the column in order to inspect ?

also can the switch be used from an 82 gas engine pickup column ?


or do they differ ?


thanks for anything