I want to say it is a gray wire with a black stripe that can be tapped at the base of the light controller stem thingy (Tech term). I will look it up tonight whan I get home. I tapped the same wire when installing a remote start to signal the engin was starting (Then I shorted the entire thing out with the last wire and could not use the unit, But it was not related to the gray wire with the black stripe........ I am 90% sure.........OK 63% sure .......... 45% of the time ........ or was it purple with a yellow stripe ....... no thats dumb .......... or .......... let me look it up).