I can't seem to find a thread pertaining to my issue, but my reverse light wiring harness is gone. The truck has a flatbed with no reverse lights so someone just undid the socket and took the whole harness out. I added reverse lights so I bought the harness to plug into the switch, but I'm not sure which wire is which. There's a black wire with a white stripe, and a purple wire with a white stripe. Is one the power and one the ground?

Any help is apreciated

 

Year, model, engine, transmission of the vehicle in question?

 

It's a 1988 Ford F-250 with the 460 and zf manual transmission