is the button on the seat?
My 97 seats have the button on the seat HOWEVER the buttom gets its power from a different source then the heater.
So first check the fuses then I would say unbolt the seat and have a look at the wiring.
if the button is on the seat then it should be pretty easy to find the problem, since there are like 3 wires that go to the entire seat.
If you have + and - where you should when you should (test with seat un bolted) then the heater istself may be FUBAR'ed