I intended to start a new thread documenting the conversion of my new seat from unheated to heated, but I think I'll just continue spewing in this one. There are plenty of videos and how-tos that show how to add a heat pad, although most use after-market products. My heat pad is OEM, out of the original drivers seat. Here's a look at it after I used spray adhesive to glue it in place on the foam seat cushion. Gluing is necessary. You don't want the pad moving around under the leather..
As you can see, I opted to go with nylon pull-ties instead of hog rings, the original method of attaching the leather to the seat cushion. I do have access to hog ring pliers and hog rings and I fully intended to use them. But after messing around with them a while I tossed them aside. My resistance to them might have something to do with what a thrash it was to remove the original hog rings. My wire cutters weren't up to the task, even though they had clipped other hog rings with no problem. Go figure. Maybe Porsche used titanium hog rings on this particular seat. I ended up using a Dremel with a metal-cutting blade instead. Pull-ties are much, much easier to deal with, You simply thread them around a wire rod at the bottom of the slit in the foam. You don't have to wrestle the foam aside and try to get hog ring pliers down there where it's hard to see what you're doing, while the leather itself fights you. You simply pull nylon loops tight. I have every confidence the pull-ties will last well into the next century. In 2124, when my 986's owner needs to replace the leather, it's a matter of merely snipping the nylon ties, no Dremel necessary.
I'm now in the process of finishing installation of the leather cover after securely zip-tying it to the foam cushion, which sits in a sculpted plastic seat base. The leather needs to be stretched around the bottom edge of the base and secured with a flexible plastic channel around the inside edge of the cover. The leather was pretty tight before I removed it. Adding a 3/8" thick heat pad to the cushion will make it even tighter. I'll need to stretch it considerably before I can secure it in place. I'm using clamps around the bottom edge to stretch it. From time to time I stretch it a little more and clamp it again. Tomorrow I'm going to try heat from a hair dryer to stretch it even more. I've also enlisted the help of a couple of manly volunteers who can compress the foam for me to give the leather yet more slack.
And I haven't even gotten to the seat back yet.