[petrel]

It really depends on how the lights you selected are set up and what condition the existing wiring is in.

I doubt you could find an entire plug and play harness for a dry box. If there is already a hot wire, I'd just install a ground, starting at the plug (so it can be connected to truck ground and also grounded to the trailer frame), then just install a dropper for each light in the run, as you go along.