I think a Harness is the way to go, I was on my way home today and the signals were all Screwed up, so I stopped by me buddys shop to try to find the problem, I was smelling burning Electric and after looking around I saw that the Pacer LED bar was MELTED!!! Quick get under the truck and remove the "Professional Install" Job buy the local Truck store(Hacker) what a **** job!! any way I saw a junction box above the hitch so I thought that I could pick up a harness for there,??heymccall;1543576; said:The extra plug should be a light green wire. Regardless, it is a brake light only wire for upfitting a cap with the federally mandated CHMSL (third brake light.) As for the four pin plug, if you have the seven pin plug, the truck should have been delivered with a four pin to seven pin adapter. The harness itself does not have the extra four pins like a ford. If your not a wire cutter, a HOPPY trailer hareness interface from your autoparts store can work, although they can be pricey.