I am wiring up some under the bed lights for plowing. I would like to know what the colors of the wires are for the rev. lights and the 12v in the trailering harness. I need to tap into those wires

 

There should be a legend on the cap of the light socket. You might consider buying a trailer light plug and wiring to it.

Use heat shrink butt connectors or heat shrink tube in either case.

Back up lights are the center pin.

marker lights are the 11 o'clock pin.

If you are installing a high draw light, install a relay.