Trailer Wiring Harness Causing Dash Warning Lights on a 2005 Toyota Highlander

Question:

Step on brake - left grren arrow on dash lights up. Turn on left signal blinker and lights on dash come on such as low tire pressure light flashes this has been checked, emergency brake light comes on and the VSC light comes one. This problem was fixed about a month ago by replacing an amber tail light. Now its back again and all the light bulbs seem o.k. Help!!!

asked by: Bessie

Expert Reply:

First let's make sure you have the proper trailer wiring harness. Tow Ready harness # 118413 is designed for all models of the 2005 Toyota Highlander EXCEPT for hybrid models. If you have a hybrid model this harness is not a correct fit. For a hybrid with factory tow package you would use # C56107.

Next check the connections where the harness plugs into the vehicle. Look for broken or bent pins. This could cause malfunctions or shorts. If you do not see anything out of the ordinary, plug the harness back into the vehicle. Make sure the harness is ground to a clean bare metal surface. No paint or corrosion at the ground location.

Something may have happened to short out the converter box when that bulb burned out. To test it you will need a circuit tester such as # PTW2993. Test the wires going into the converter from the vehicle. If you get the proper signals going into the box but not coming out of the box on the 4-Way side then there is something wrong with the harness and it will need to be replaced.

If the signals are not correct going into the box, remove the harness and plug the vehicle lights up like normal. If the problem stops that indicates an issue with the converter box and it will need to be replaced. I the problem persists then the issue is on the vehicle and should be checked out by a Toyota technician.

expert reply by: Michael H