When Connecting Trailer With 5-Wire Harness To 2010 Toyota Highlander Left Side Lights Not Working

Question:

5 wires coming out of the trailer into a 4 pole connector, White gnd, yellow, green, yellow/brown and green/brown. I connected the yellow/brown and green/brown together to the brown going into the plug on the trailer. 4 pole plug on the car dealer installed. wht. green, yellow and brown. electrical short in the car with smoke ! right side trailer worked, left did not. I tested the trailer lights individually with a 12 v battery all are working, running lights, tail lights on brown wire OK, green wire for the right side and yellow on the left side worked as well. put the white wire onto the neg terminal of the battery, individually tested each of the colored wires by touching the positive terminal.

asked by: Michael B

Expert Reply:

It sounds like you have a short on your boat trailer wiring harness on the left side. When you are testing the lights on the trailer with just the 12-volt battery you are eliminating the ground on the trailer frame, so the lights will show that they are all working on the trailer.

I would recommend rewiring the trailer with the Optronics 35 ft. Wishbone 4-Way Trailer Wiring Harness # A35W42B. This harness has the 4-way connector with a 5-wire system. This will eliminate any possible shorts from happening on your boat trailer.

Sometimes when you get a short on one side of the trailer it is possible that you could be close to having a short somewhere else on the trailer. On a boat trailer the wires are usually ran on the inside of the trailer frame and over time the wires could be rubbing against the frame and cause a wire to become bare and touch the frame.

If your trailer wiring harness is inside the boat trailer frame you can install the new Optronics wiring harness by using the old harness as a fish wire. Attach the new harness to the old wiring harness and as you pull out the old harness you will be installing the new wiring harness in its place.

As far as the short and smoke in your 2010 Toyota Highlander you will want to check the towing fuse location on your fuse block to make sure that the fuse for towing is not damaged and also check the fuses for your left turn and brake lights.

You will also want to check the black converter box on your vehicle, which is part of the trailer wiring harness, to make sure the short has not damaged the converter box. You can use a circuit tester like # PTW2993 and test the wires going into the box for a signal and then test the wires coming out of the box for a signal.

If you have a signal going into the box, but not coming out, then the converter is bad and will need to be replaced. Also, check if there are any in-line fuses on the harness that are not damaged.

The wiring harness with converter box for your 2010 Toyota Highlander is the Tow Ready T-One Wiring Harness # 118449. I am sending a link to the instructions on this harness and a video link of the harness being installed on a 2010 Toyota Highlander.