Here are the ones I used. Innovative Heat II
despite what is says it takes longer to get warm than 2-5 minutes. They really won't heat up until you sitting on them for about 5 minutes. I've let my truck run for 15 minutes and still got in to cold seats in the winter. For me they get really toasty on high when they kick in but my wife says they are not hot enough for her. Then again the Tahoe seats will cook a steak! If you want some heat get these Innovative Heat MD
they are $70 more per seat but I wish I would have got them. They have a selectable switch with 5 settings. Mine only has hi and low.