How to Wire a Car Trailer

Wiring up a car trailer is necessary for the trailer lights to work in unison with the tow vehicle lights. While it is not a complicated procedure, you'll need to put some thought into it; the wires must connect to the corresponding vehicle wiring in order to be work properly. Plan ahead; decide which type of connector you want for the link between the tow vehicle and trailer and the process will go much smoother.

Things You'll Need

• Wire or trailer wiring harness
• Terminal connectors
• Wire strippers
• Trailer to vehicle connecting plug
• Loom (optional)

Instructions

1. Connect the new wiring to the trailer lights. The lights will have wires coming out of the back of them that must be extended to the tongue of the trailer in order to connect to the tow vehicle. Carefully measure and cut each new wire so that they aren't too long or too short, and connect them to the wires on the trailer lights using terminal barrel connectors and crimpers. The wires are color coded, so if possible, acquire wire of the same color as that coming out of the trailer lights so there is no confusion when attaching to the tow connector. Generally, green is used for the right stop and turn function, and yellow for the left stop and turn. Brown is used for the license plate and any marker lights that the trailer may have, and white is used to ground. If you use all one color, label each wire carefully so that the right wire goes to the right spot.

2. Route the wires along the trailer and to the tongue. Of course, you will want to take great care when routing the trailer light wiring. If it is allowed to chafe the insulation could wear off, leaving bare wires that could cause an electrical short in the tow vehicle. Many people choose to run the wiring inside a plastic loom found at any auto parts store for added protection. If at all possible, run the wiring through the frame of the trailer. If that isn't an option, run it very high and tight along the frame where it will be in the least amount of danger.

3. Splice the wires into the trailer/tow vehicle connector. Do this in the same manner as the trailer lights, using butt connectors and wire crimpers. Make sure you pay very close attention to the coloring and labeling of the wires, so that they get connected to the correct terminals.

Tips & Warnings

• Always test the lights before towing to make sure all stop, turn and tail functions are working.

References

• Types of Couplers and Diagrams