How to Wire Boat Trailer Lights by Will Charpentier . The connections are made to the tail light wiring harness at the lights or under the bumper, and the quick connect provides the junction between this point and the trailer's wiring. Again, use the probe on the test light to find the tail light wire that lights the bulb of the test. Disconnect the trailer from the vehicle and run a test to determine if the trailer lights function properly. Wire the vehicle side wiring harness to a standalone battery. All you have to do is link up the white wire to the negative and the colored wires to the positive.. To test this connection point, turn on the vehicle's running lights and connect the test bulb between this point on the frame and the brown wire pin on the vehicle jack. The light should come on. If this connection point is good, then check for an open or broken ground wire..
Amazon.com: trailer light wiring harness. From The Community. Amazon Try Prime All lights and wiring harness Large 4.5 light and bracket Trailer HQAP Trailer Wiring Harness Kit 4-Way Flat Wishbone-Style With 4 Flat Connector for Under or Over 80" Wide Trailers. by HQAP.. How To Fix Your Trailer Lights. We have written this to make it easy for anyone to understand and test trailer lights. Feel free to print this document and wiring diagrams to take them out in the shop or driveway to help you find and fix the problem.. Whether you have just installed a new vehicle-to-trailer wiring harness or are trying to locate the cause of an electrical problem,Trailer Light Tester is great for testing tail lights, turn signals,.