I need to know the colors of my tail light, brake light Mar 15, 2010I need to know the colors of my tail light, brake light and. Rear park lamp wire is brown. Rear brake lamp wire is light blue. Left rear turn signal wire is yellow. Right rear turn siganal wire is dark green. Ground wire is black. What is the Factory Wiring Harness Color Code for a 2007 The colors that GM typically uses for their factory trailer wiring are as follows -. Dark Green - Right Turn/Brake Lights. Yellow - Left Turn/Brake Lights. Brown - Tail Lights. White - Ground. Light Green - Backup Lights. Blue - Electric Brakes. Red/Black - 12 Volt Power.