4-pole to 5-pole tow wire harness kit installation

[TestEngr]

I have a 2009 Highlander, 4X4 with tow package. The Class III hitch and 4-pole harness was installed by the Toyota dealer. The trailer I'm towing has surge brakes, and the trailer harness is a 5-pole connection. There is a kit available to install an adapter that will adapt the existing 4-pole flat connector to a 5-pole flat connector. It's fairly straight forward to install, however, I need to splice in one wire from the kit into the rear back-up light on the Highlander. This is so when the transmission is shifted into reverse, the back up light circuit will energize the surge brake solenoid and allow me to back up the trailer.

When I pulled off the back-up light on the Highlander, there are two wires that come off the bulb. One is the color blue, while the other is the color white with a black stripe. One of these is the positive, and the other is ground, but I do not know which color is which. I need to slice the trailer wire into positive.

I know it's a long explanation and thanks for taking the time to read it, but does anyone know which of these two colored wires is positive and which is ground?

Thanks for your help.

[Judy H]

Ues a test light to check and see which one lights up, when you stick the wire with the point of the light tester. The ground will not light up, and the positive will light. Hope this helps.
~Judy in MI~
I just put a trailer wiring kit on mine, used a test light to tell which was positive. I`m came with the towing hitch, but no wires to be found.

[Judy H]

Okay, looked in my book which covers only HL 01 thru 06 and the white/black shows hot. Not sure if they changed to wiring between 06 up to 09?
Hope this helps
Mine did not come with the pig tail. Only took me less than half an hour to install.
It took longer to get to the wires, etc , then it did to do the work.
~Judy in MI~ This book also covers the Lexus RX 300/330 99 thru 06


01 HL V6 4WD
97 Tacoma V6 4x4
88 Tacoma V6 4x4 stick

[TestEngr]

Originally Posted by Judy H

Ues a test light to check and see which one lights up, when you stick the wire with the point of the light tester. The ground will not light up, and the positive will light. Hope this helps.
~Judy in MI~
I just put a trailer wiring kit on mine, used a test light to tell which was positive. I`m came with the towing hitch, but no wires to be found.

Thanks, Judy. I do not have a tester to check for the hot wire, and I was trying to avoid buying one and see if anyone knew which wire was hot. I had a suspiction that the blue wire was ground, but I guess I need to buy a test to make sure.