Similar issue on an E-150 Chateau. I am getting 8 Volts for my Running Lights and Turn Indicators for the trailer. Have measured voltage at the back of the truck, intermediate wiring harness and in the engine compartment at the Power Module Fuse Box. The trailer is not connected, so the issue is not there. It seems I am getting some resistance in the line and have no clue where to look now. I am not losing the car battery and get 12.5 V when I check it directly. What else is inline here that I need to examine to find the source of the voltage drop? | 
