When I did this to my trailer I found the wires coming from the harness inside the front compartment on the right hand side. To convert to turn signals you will need this converter.
http://www.drawtite-hitches.com/wiring_converters.htm
The stock wire from the lights I found inside the propane compartment. If you reach in you can feel the wire coming from the light.
Make sure that the wires are connected correctly, as I had got might crossed, in the small space working on them. The lights worked fine, but when I went to leave it was sending a signal to the truck that the brakes were not working and would not let me start the truck.
The wiring loom from the pin box runs down right next to the batteries and then into the belly, in a 1" black plastic split conduit. Just reach in the conduit by the batteries and find the green and red loose wires (left and right turn). Verify with a test light. T-Tap those wires with leads from the converter marked for left turn/stop and right turn/stop (T-Tap: connect to the factory wires, but let them continue to carry current to the factory tailights). The converter input also has a third wire for ground which I grounded with the battery cable ground on the frame right next to where you are working.
Output on the converter is left turn, right turn, and stop. The stop wire is not used and should be taped or protected from grounding. The left and right output wires go up to the frame in the front of the compartment, then straight out to the LP compartments where the forward marker lights are. Remove the 2-wire marker lights and replace with your new 3-wire midturn lights (ground, marker, turn).
Linear Mode
