I have a 02 Ssei bonneville with leather interior it came factory without heated leather interior If I find a salvaged ssei 02 with heated seats whats involved removing seats an wiring and installing in mine?

Aside removing the seat, you are going to need remove all the wiring from the seat to its power source. I believe the heater timer is not built into the seat, rather its located else where. Plus the switch itself is I believe mounted in the center console.

Probably would be easier to get the heater pads that you just strap to the seat. But I know I know. My Bonneville has the cheap leather seats and they are a BEAR to sit on when its 5 degrees out.

You could try ordering these: Custom Fit Heated or Massage Seat Kit - PFYC.com