4 Wire Round Trailer Plug Diagram. Cut the white wire short enough for attachment to the front of the trailer near the connector plug. The white wire must be attached to the trailer in order to ground and power the lights.
Not sure which wires attach to what on your trailer connectors? As a professional trailer parts exporter in China, we have all kinds of trailer parts. such as trailer plug and socket, trailer light and lamp, trailer jack, trailer coupler, trailer axle, trailer. So here I have an older trailer which needed some work Perhaps you want to add clearance lights, extended the plug length at the tongues end, change out And the third diagram using clearance lights.
You don't know if the wiring is bad or you have bad bulbs.
Un plug the connector at the taillight and turn the truck side so you are looking into the plug.
Cut the white wire short enough for attachment to the front of the trailer near the connector plug. Learn all about trailer wiring at HowStuffWorks. Not sure which wires attach to what on your trailer connectors?