There isn't as much info about the Heat Demon seat pad as compared to the grips. For the installation, you need to first remove your existing seat cover (obviously!). This will take some time since there are quite a few staples holding it on:
You will need to pry the staples up slightly and then pull each one with a pair of pliers. I found that a sharp chisel worked well for the prying part. The edge can be carefully worked under the staples, and one side can then be lifted up. They are in pretty tight, so again, this takes some patience. When you're all done you will have a pile that looks something like this:
Once the cover is off, you will want to carefully locate where the heated pad will be stuck onto the seat. The pad itself is adhesive backed, so once placed it will stay put:
The seat cover is fairly wide and not perfectly shaped for our Grizzly seats. It would be ideal for the pad not to break over the top surface of the seat and down the sides, as it does toward the front. You could move the seat pad back further, but in order to clear the edges, it's just too far back. It would heat a rear passenger, but your own ass would be ice cold.
It's too late for me, but I did come up with an alternative way that I could have done this to avoid this issue. It's not super easy to see in the picture above, but the wire exits the heating pad at front center. The wire then heads down through the seat (more on that in a minute) and out the underside. After I had already drilled the hole and adhered the pad to the seat, I discovered that you can actually cut this pad to shape. But, the cutting has to be done at the rear of the pad (opposite side from where the wire comes out) to prevent cutting the element in a way that will kill it. So, had I known that, I could have rotated it 180 degrees, cut the pad to be more narrow and shaped similarly to the seat, scooted it up a little more, and all without it breaking over the top surface and down the sides.
Anyhow, more on passing the wire through the seat. I did this with a large Philips screw driver and a hand drill. The drill is only for putting a hole through the hard plastic on the underside of the seat. Don't bother trying to drill through the cushion. The screwdriver is best for that part. From the top side, carefully force the screwdriver down through the cushion and toward the exit hole you drilled in the underside of the seat. Starting from the topside guarantees that the hole is right where you need it so the pad ends up where you planned. If you work from the bottom side, you might not end up with the hole exactly where you wanted it.
After you have the hole taken care of, remove the screw driver, and now go to the underside and force it back through the hole you already established. Tape your wire to the screw driver (use plenty of tape) and fish it back through, like this:
The seat pad also comes with what looks to be 1/4 adhesive backed foam padding. Cut it to shape as needed and place it over the heat pad:
Ok, all that was the easy part. Putting the seat cover back on, IMHO, is the harder part. Don't bother with a manual spring action hand stapler. The plastic is too hard, and it will not set the staples. Ask me how I know😉
Instead, use a pneumatic stapler (you can get a decent one on Amazon pretty cheap). They work really well and make this job MUCH easier. 89Sandman (on this forum) gave me some good advice for installing the seat cover. You want to secure a few staples at the center of the backside, then a few at the center of the front side. Then work back and forth down the sides. It takes some practice and I had to pull several staples to realign and get things right.
I went with w RoxSpeed cover rather than putting the OEM one back on, but there is no reason you can't reapply the OEM cover.
Here it is after patiently putting 100 or so staples back in (the rear rack is off the bike in this picture since I was working on some custom rack mounts at the time--they are almost done so more on that later, too):