TomatoSoup installed them here for the solstice.
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Transfering my post from the ModMeet thread (and adding a bit more)...
I got the exact same Peak Universal 9" x 18" kits as Joe is posting about.
I did both seats and used both heater pads on each - even over the Airbag sensor on the passenger seat base. Covering this sensor is apparently not recommended by GM but I've had no problems with the sensors working with various people in the car (so far) - having said that I
TAKE NO RESPONSIBILITY for anyone else's installation! Note: you actually
must use both pads/seat if you want the dual temperature operation. The way they work is that the kits have relays that switch the 2 heating elements per side (seat bottom + back) either in parallel for high heat, or series for low heat. If you use only one pad, you'll only be able use the high heat position.
The kit comes with pretty much everything... only issue was the wiring loom wasn't long enough the way I installed them, so I had to splice some wire extensions in. I had mounted my relays alongside the Onstar box under the waterfall and had to use a couple of feet extension of three wires each side (from the relays to the seats pads) and a couple more feet of 4 wires (each) to the switches mounted above the radio. There's probably a better place to mount the relays though (inside the seats maybe?) that will remove or reduce the need for extensions. Bring wire just in case?
Another point is that we/someone should
get a supply of those "christmas tree" retaining clip/plugs for the seat coverings - you WILL destroy some of them when you remove the seat covers!
EDIT: For those of you who propose to do this, you should brush-up on the seat and cover removal tips in JPM's post:
http://www.solsticeforum.com/forum/f11/fix-saggy-seat-some-diy-jpm-46877/ This skips the final step of removing the back cover, but that's just an extra step that involves prying off the backrest tilt lever button. Plus, you
may not need to fully remove the back cover anyway but just slide it up enough for access (I'm not sure 'cos I DID remove it fully when I did mine). Also there was a link on JPM's site somewhere that documents how to replace the seat covers. That has all the steps to fully remove back and bottom.