Not recommended for everyone, but if you want to save the money over what a heated seat costs or what installers charge to convert a regular seat to heated, this has worked for me. Have done several, from about 3 years ago. All working fine.
Used this kit from Amazon:
https://www.amazon.com/WATERCARBON-Premium-Heated-Seat-Kit/dp/B00AKFFR6C/ref=sr_1_37?ie=UTF8&qid=1477597410&sr=8-37&keywords=heated+seatSeat cover off, install heater pad over foam cushion but under plastic liner. 2 elements - 1 for rider, 1 for passenger. If plastic tears a dry cleaner plastic bag can be trimmed to fit over foam on seat. Heater elements
must be installed under plastic.
Cut hole in side of outer seat material for switch. Added seat material to switch itself so that it could be glued to the inside of hole, leaving room for switch to show. Do not cut out fuse from wiring harness, fuse
MUST be used! Wire straight to battery or use Deutsch plug, and follow directions for wire connections. Check to make sure all works ok.
Reinstall outer seat cover. A staple gun works great, be sure to stretch tight, should re-align as it was originally. Seat will heat up in 2-5 minutes. 3 position switch - Low, Off, High. Kit was designed for car use but works fine for MC seats as long as plastic is used over heater elements. Start to finish takes about 2 hours or so. Can use Deutsch plug (unused on many bikes) near bike battery if you wish to run off ACC switch, but will need the mate to the Deutsch plug and wire in to that mate plug instead of straight to battery.