The wires are Battery positive and Battery negative (aka ground - it can be connected to the chassis most anywhere but best to run direct to the engine ground post that the battery connects to) and marker light. The marker light can be tied into the trailer lights wiring. The trailer light wire bundle can be found under the chassis and tapped into, or you can get it at near the fuse box or at the connector itself at the rear bumper. One will be for trailer running lights, others for left, right turn, brake, and reverse (backup). May have others for charging power. Thre are other ways to get this as well, such as run a new power relay's coil off any ignition switched circuit.
Search for trailer connector (4, 5, 7+ pin RV connector) that matches your plug or you can look in the Ford manuals. You can find what pin does what function. In the case of my RAM I found the Dodge body builders guide and it has the cable routing plan so I knew where to tap into the bundle and what wire color to look for, under the chassis near my camper connector for a short run.
