What year truck? I did it and the auto dimming mirror in my 02. You need the computer and the pigtail from it. It's 4 wires. I left my stock plug to the lights alone and ran the 4 wires down the a pillar to the fuse box. A fuse tap is perfect for the 12v need a ground the orange wire goes to the dimmer and you need to tap into the violet/yellow wire at the CTM. I used a quick splice for that it worked perfect. The mirror is 3 wires but I only did 12v and a ground. The third wire is supposed to be hot when the truck is in reverse that way it isn't dimmed when you are backing up. I didn't worry with that and haven't had a problem at all