Chevrolet Repair: a/c heater wiring schematic, chevy garage, resistor pack

Question
R&R a/c heatercore,evaporator,recharge(r12)system running fine. Fan switch broke,whole system shut down(astro vent included) replaced fan switch and the blower. Nothing. Found blown fuse, replaced, still nothing.Replaced the relay, nothing.Need to know the wiring diagram and how to check the continuity of the associated parts. Can not find any burnt wires. Have had this old truck a long time. 1979 Silverado 4X4, 3/4 ton on 1ton chasis,350 CI. Please help. The local Chevy garage won't because of the age.

Answer
Hello Becki,
I looked at the truck across the street, and the resistor pack is under the hood, on the right side of the blower housing. Only 4 or 5 wires.
There is a separate ground wire to the blower motor, actually under one of the mounting screws.
Run a jumper wire from battery pos, to the blower pos terminal to test the continuity and effectivness of the ground. It should run full speed.

Van