7 Pin Trailer Wiring - Color Codes There are seven different electrical wires that connect and sync the 7 pin trailer connector with your vehicle. That said, the wiring harness in the majority of vehicles will contain eight different wires, and sometimes even more.. This document outlines the installation of a 7-pin trailer harness on a 2021 Toyota highlander (2GR-FKS). The brake controller that was installed is the "Redarc Tow-Pro Elite V3". This highlander already had the OEM 4-pin towing package installed which provides turn/brake signals, running Lights and a ground connection. To add a 7-pin harness there are three additional wires required.
I was adding an extra 4 pin connector behind the back bumper, so I could plug in my aftermarket LED blinker/stop/tail light strip, and not have to unplug it when I plug in my 4 pin trailer harness. This is what you'll need to know if you ever want to tap into the wires that feed the 7 pin connector. I drew this crude diagram to help explain.. A Toyota 7 pin trailer plug wiring diagram is a technical schematic detailing the specific pin assignments and wire colors used to interface a Toyota vehicle's electrical system with a trailer.