I ordered these as a replacement for my stock, heated, signal light mirrors on my 2008 GMC Sierra. I wanted some tow mirrors that I don't have take off and put on everytime I take my camper someplace. I'd like to buy a new truck with tow mirrors but of course the prices are ridiculus. When I pulled them out of the box they were packed pretty snug in formed styrofoam. The two mirrors, a bag with nuts to mount the mirrors, two replacement triangle foam pieces and another bag that had two pairs of black/red combo wire with a small connector on on end and two round electrical connectors. I scratched my head. I looked at the mirrors and see the standard plug for the wiring harness in the door/switch. I also seen a little plug at the mirror base which I assumed was for the red/black wires. But no instructions of any kind.I removed my passenger side door panel first. Took about 5 minutes. At first I scratched my head because the stock mirrors had two harnesses that come from the mirror and plugged into the door's control switch. I looked at the new mirrors and there's only one. Hmmm. I removed the old mirror and old piece of foam from the outside. You can actually unscrew the three nuts holding the mirror in place then on the outside give it a quick forcefull down hit and the mirror will pop off. There's a clip that holds the mirror in place.Before I put the mirrors on I hooked up the red/black wire to the small connector on the mirror base. I knew it had to be for something. Then I came back here to see if anyone could tell me what they were for. In all the comments here people said it was for the reverse lights. But then others said for heated mirrors. Well it's acutally for the reverse lights. The black gets grounded somewhere, hence the round electrical connector to attach to a screw. The red wire gets fished thru the door and body and either goes thru your firewall to the reverse lights in the fuse box or gets routed inside the truck to your reverse ligthts or as someone else had done to your interior dome lights. I have done nothing with them yet. The wires are coiled up in the foot panels on each side of the interior cab.I Next I put the new foam on the outside and put the mirror in place. I had my grandson hold the mirror while I put the three nuts on and tightend them up. I grabbed the door switch and plugged everything in. I started the truck and checked the function of the mirrors. The turn signals worked as they should and the mirror adjustment worked as it should too. I didn't check the heat function but hoping this will work in a few short months when it gets colder.I fished the red/black wire thru the door, down and thru the rubber boot the wiring harness goes thru the door and truck cab. I rolled these up and pushed them into the side panel. I'll tackle that another day. I put the door panel back on and did notice the wiring harness from the mirrors to the switch is a little short but not enough to stop me from hooking up the door switch. I got everything all put back togeather and they looked pretty nice. I proceed to do the driver's side. No issues. It took me an hour to put both of these mirrors on.Now the shortcomings... The mirrors vibrate. It's tolerable but they vibrate when driving down the road. Somehow the manufacturer needs to stop the vibration on these mirrors. I have some ideas on how I can get mine to vibrate less but not sure if I can get them to stop completely.Secondly, they need to include instructions on what the red/black wire's are for. We can't read minds.Third, make the wiring harness from the mirror to the door/switch longer. Add an extra 6 inches to work with so it can be routed just like the OEM wiring harness from the mirror to the door/switch.Would I recommend these. Yes as a cheaper solution then spending $500-600 on other mirrors. But the most important thing I believe is fixing the mirror/glass vibration. Like I said, it's tolerable but not how they should be. The mirrors are manually retractable which I don't see as a problem. They do what I want them to do.