by David R. Wetzel
Four Wire Trailer Light Connectors – The typical connection type used for pulling small to medium boat trailers and small utility trailers. This installation is designed for most trailer connectors in four wiring situations. See tips for vehicles that may have a five-wire taillight system. Installation should take less than an hour.
Find the wiring harness for the taillight, which is typically located inside the trunk near the rear bumper.
Locate a suitable location for the harness clamp for the four-wire trailer light connector and harness under the rear bumper area. Drill a 1/8-inch hole in the car frame near this location and secure the wiring harness clamp for the light connector with a sheet metal screw.
Leave approximately 6 inches of the end wire harness with the connector hanging loosely from the wire harness clamp.
Drill a 1/2-inch hole in the bottom of the trunk near where the wiring harness for the four trailer lights will connect to the wiring harness for the tail light.
Push the other end (not the connector end) of the wiring harness through the 1/2-inch hole in the trunk.
Find the green wire in the right side taillight wiring harness, stop and turn the light on. Use a wire splice to connect the green wire from the four-wire trailer light connector harness to the green wire from the tail light.
Find the yellow wire on the left side taillight harness, stop and turn the light on. Use a wire splice to connect the yellow wire from the four-wire trailer light connector harness to the yellow wire from the tail light.
Find the brown wire in the tail light wiring harness for the tail, license plate, and position lights. Use a wire splice to connect the brown wire from the four-wire trailer light connector harness to the brown wire from the taillight.
Drill a 1/8-inch hole in an exposed section of the metal frame inside the trunk. Use sandpaper to sand the metal within about 1/2 inch of the 1/8 inch hole. Sand until all paint and other materials are removed and only shiny metal remains. Connect the white wire from the four-wire trailer light harness.
Attach the white wire, ground wire, to the 1/8 inch hole with a sheet metal screw.
Test the wiring connections by turning on the headlights. Attach the ground side of the test light to the ground wire connection screw.
Glue the pointed end of the test light onto the green wire of the four-wire trailer light harness. If the test light is on, the connection is good. Turn off the headlights.
Turn on the right side turn signal, if the test light flashes, the connection is good. Have someone step on the vehicle’s brake pedal, if the test light comes on, the connection is good.
Repeat the last two steps for the left side using the yellow wire from the four wire trailer light harness.
Seal the 1/2-inch hole in the log with silicone to prevent water from entering. Cover the ground connection (white wire) to the frame with silicone to prevent oxidation.
- Make sure none of the cables rub against the metal edge of the 1/2-inch hole drilled in the trunk.
- If any lights are not working properly, check your connections.
- Please do not seal anything with silicone until the wiring is complete, to avoid scraping the silicone, which is a mess.
- Some vehicles have a 5-wire system and it is necessary to purchase a trailer light converter that matches the trailer’s 4-wire system to the vehicle’s wiring system. The converter is available at most auto parts stores. The converter comes with a wiring diagram.
Articles will need
- 4-wire trailer light connector and harness
- 12 VDC test light
- Punch out
- 1/8 inch bit
- 1/2 inch drill bit
- Silicone tube
- 1/8-inch sheet metal screws
- Cutter / Stripper
- Wire splices