You need to replace the heater pad that is sewn into the seat cover. It is possible to replace the pad with an aftermarket one without sewing but it will not go up the side bolsters like the original. Still works almost as good!
I think KevinKay was going to do a post with some pics when he did his, not sure if he got around to it yet. Do not replace the hog rings as I think that they are what shorts out the element, use zip ties instead.