Hi Mike . . .
Welcome aboard. If the truck were mine I would invest in a Shop Manual. They are available in reprint and will include a wiring a diagram.
There is nothing particularly tricky about positive ground systems - they just fell out use as the auto world standardized on negative grounding.
In terms of the wiring harness (like everything from this era) if there is a wire it is hot, with grounding coming from the body, frame or engine to complete a circuit. The only connection from the + post on the battery will be to the frame or engine-block.
From an electrician's perspective - ground is just a reference. On a 6-volt negative grounded system hot wires carry +6-volts, on positive grounded system hot wires carry -6-volts.
regards,
stock49
