The seat heater kit was purchased from Check Corporation.  The kit, UNV-27, was $75 for each front seat, including two elements (one for your butt, one for the small of your back), switch, relay, harness, and all kinds of fuse taps/tie wraps/doodads.  The elements are very thin and have an adhesive to hold them in position.  Removal of the upholstery is only required for the butt cushion - but it's a bitch!  Many little hogrings that need to be split open w/ pliers and a screwdriver!

The heaters take about 3 minutes to reach full temp, not as fast as I had hoped, but WOW! do these things get HOT!!
There is a Hi/Low setting w/ a timer that turns off the heater after 10 minutes.
Some folks may consider it a waste of money, but I like them.  $150 is steep though for butt warmers.....

Installation is as follows: 4 hrs / 6 beers (It was cold...)

1. Remove the seats from the vehicle
       Two bolts in front, two bolts in back, and the seat motor wiring connector in front

2. Remove the butt cushion from the seat frame
       There are two large retaining bolts in the rear and two in the front

3. Install the back element
       Release the tension on the lower upholstery by pulling down at the bottom of the map pocket.         The fastener is held by a lip/J-channel at the bottom.    Pretty easy - no hogrings to remove.
       Just peel and position the elemen in place and stick!  

4. Turn over the butt cushion and begin removing the hogrings around the front, back, and sides.         Pull loose the cover from around the edges to expose the hogrings that hold the seating area seams down.  These are really tough to get free.  They run lengthwise and transverse across the seating area.  Take only one side and the transverse section free.  There is no need to remove the entire seat cover from the cushion when it's not entirely necessary.

5. Peel the backing off the element and place it on the cushion making sure the opening in the element corresponds w/ the crease in the cushion.  Route the harness to the rear of the cushion.

6. Begin the arduous task of re-attaching the hogrings on the seat cushion.  Be careful not to pull the steel reinforcement rod out of the seat foam molding!

7. Reattach the hogrings around the perimeter of the seat cushion.

8. Mount the relay/timer in an unobtrusive location, making sure the movement/travel of the seat will not come into contact w/ the module.  I found a spot under the seat attached to the frame that cleared the seat and also my CD changer mounted underneath.

9. Connect the back element connector to the butt element connector and then to the relay/timer module.  The main power connector attaches to the relay/timer module as well, and does the switch.

10. I ran the power wiring under the carpet to the fuse block under the drivers dash.  I ran each seat  to a different fuse.  Each seat has a 7A fuse and I did not want to combine both seats for a 14A load on an existing 15A fuse, instead I used the supplied fuse taps on the "Accessory" and "Wiper" fuses.  Both of these are only hot when the ignition is ON, so I don't have to worry about forgetting to turn off the heaters and draining the battery!

11. Reinstall the seats.

12. I chose to move my ECT switch on the console to an upper position across from the rear window switch, which opened up the two lower positions for the heater switches.  The switches are not quite factory sized, but close.  They are slightly wider, but about 1/2" shorter that the Toyota switches (Landcruisers have nice lighted factory switches that I'm going to see if they fit)  Using a Dremel tool w/ a small fine sanding drum, I carefully narrowed the switch to fit the console opening.  I then took the factory "blank" and cut it to fill in the gap left by the shorter switch.  I was careful to slowly adjust the length of the filler piece in order to have a tight, almost seamless fit.