they are tuff trucks.
but like said..look at the drip rail/kick panels/floors/cab corners/rockers
also look at the frame for cracks at the steering box.
wire harness needs a look at if it has been hacked up any. look for burnt fusable links at the big rubber connector and follow each fusable wire for the charging system/IGN. system/ headlight wiring all on inner fender/firewall area.
FYI when looking for replacement harness pieces the plug connectors changed to a weather proof style and 82-85 do not inter change.
bad spot on the head light switch is the rivet that holds the spade to switch, they get loose/hot/burn/melt plug & switch.
if mech linkage on clutch have a look at rods/torque rod to see if bushings/clips are shot or eyeholes in rods are not wallowed out and sloppy.
have a look under the chassis for oil seepage/leaks at the rear main seal
trans seals/pto covers/pinion seals/axle seals.