How To Wire Your Car for Trailer Lights

Trailer wiring kit

Before wiring your car for trailer lights, it is better to check if you will need to set trailer brakes too. Some trailers which weigh over 1,500 lbs need brakes. Use safety precautions before you start working. Do not use tools which will put you and your vehicle at risk or tools which will reduce the performance of your car.

Several tools are required for wiring trailer lights into your car. These include a 12V test light, a heavy duty 12V flasher, wire crimper or pliers, a wiring kit, a trailer light connector, and electrical tape. A trailer light converter is sometimes required for 5-wired car systems. Wiring manuals for trailer light converters are included when you buy one. A strong turn signal flasher is an option. It is used to transmit the extra electrical load of the trailer lights.

Some newer models of cars have wiring connectors that are used in rear lights wiring. These wiring connectors are also used in connecting trailer lights by simply unplugging the connector from the rear lights wiring and connecting it to the trailer's harness.
Few cars and trailers have 7-way connectors. The brake wires (usually blue), battery wires (usually red), and back-up wires (usually violet) are used in these connectors. There are manuals included upon purchase for 7-way connectors to aid you in connecting these.

Wiring your car for trailer lights require several steps. Here are the steps for trailer lights using 4-way connectors:

  1. Locate the position of the tail light wiring harness. Usually, tail light wiring is located inside the trunk or somewhere near the bumper.
  2. Attach the quick connect harness to a suitable location. The harness must be long enough to reach the trailer’s connector.
  3. Connect the test light’s clip end to a good, dirt-free metal chassis ground. Once connected, turn the headlight switch on (head lamp/parking lamp). Using the test light, check the wires until the light turns on and stays on.
  4. Next, connect the right tail signal or stoplights wire (usually green) using a connector. Make sure to switch off the headlights after connecting them. Turn the ignition on and trigger the right turn signal. Check the wires if the light doesn’t flash.
  5. Connect the left turn signal or stoplights wire (usually yellow) using a connector. Switch on the left turn signal. Check the wires if the light doesn’t flash.
  6. Turn the ignition off then connect the tail light or parking lights wire (usually brown). Verify by turning the tail light or parking lights on. Check the wires if the lights do not flash.
  7. Connect the common ground wire (usually white) on a metal chassis ground or existing ground wire using a sheet metal screw or a bolt.
  8. Fasten the harness into the trailer’s connector. Switch on the lights for a final test. Secure the wires with electrical tape to make sure that they aren’t loose. Connect the wired trailer connector in the trunk or underneath the car.


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