I did the heated mirror mod this weekend using the Burco RediHeat heating elements. Each cost $25, $50 total. I used a defrost switch from a late 90's 4runner. This switch is an on/off switch, I plan to do a future mod and take out the spring to make it a momentary switch. This will then trigger a 555 timer circuit to turn off after 10 minutes. I tried to make a 555 circuit and couldn't get it right so thats for another day. I found a few kits online which I may pick up.
There doesn't seem to be a left and right element. I used burco #3804 element which works great for the drivers side. The problem is that the passenger side didn't fit so it needed to be cut (which says in the instructions is ok to do), after I cut it I got no heat... So I am going back to likely get a smaller element #3801 for the passenger side. http://www.burcoinc.com/Related_Products/redi_heat.htm
I will assume you can find out how to take off the mirror and door panel...
Take the mirror out of the mirror assembly by carefully prying on the bottom side of the mirror. Then dissemble the mirror assembly as shown below.
Instructions do not say what gauge wire to use.... I used 18 gauge wire. Cut two wires about the length from the mirror to the middle of door. Tape them together the entire length and snake them through the mirror assembly as shown. Put the assembly back together, attach the crimp connections (supplied). Make sure to pull all the slack from the existing mirror harness or it will not reach the connection when you put it back. Tape the wires where they exit the mirror assembly.
The mirror is attached to a black plastic backing. I heated an oven to 300 degrees and put the mirror in the oven for 1-2 minutes. This made the plastic flexible so the mirror popped out easy. Peal the paper/foam off the mirror and clean off the glue with whatever cleaner you have (I used acetone). Try to save the foam part to reinstall. DO NOT SCRAPE THE MIRROR WITH A TOOL it will show through the mirror!
Once you have cleaned off the mirror stick the Redi Heat pad on, my foam pad still had sticky on it so I stuck it to the redi heat pad as shown below
You will have to cut the plastic backing so the connections will fit through, I used a Dremel tool. Put the plastic backing in the oven to soften it and pop the mirror back in.
Hook up the connections, (be very careful they can rip easy!) and reinstall the mirror into the mirror assembly. Its a good idea to test the element before you put everything back together.
Reinstall the mirror, snake the wires through the door. Ground one of the wires, I used the window track bolt and make sure to scuff the paint. Disconnect the door side of the rubber boot between the door and the cab. Fish a wire from the cab through the boot and into the door (the yellow wire behind the plastic in the pic below). I used a quick disconnect crimp connection incase I had to remove the mirror in the future, which is tucked behind the stock mirror harness in the pic below.
Do the same for the other mirror and run the wire behind the dash. I did not have to remove any panels except for the door panels. I used a circuit extender from the fuse block to power the switch (use a key switched circuit). I had to dremel the dash a little to fit the switch in. Wire up the switch and you are in business. Photos below are on and off. Like I said I want to add a timer so future mod to come.
Have a beer (for those of age anyway) Easy mod would do it again. Now have to wait til winter for the real test!