I'm not sure about the 73 up trucks..
my truck the one wire that powers the cab.. goes from the battery(p****ide) across the coresupport(radator) and to the voltage regulator(behind drivers side headlights, then toward the cab bulk head connector..
I'd copy and paste your question here
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in the 73-87 truck section..
and you'll get people that have seen the normal problem areas in those trucks..
where the fuseable link is (mine is on pass side fender) if you shorted out something you could take it out.. and it can come and go..