Heated Seat Problem

[03-Avalanche]

I Just purchased an 03 Avalanche with Heated seats. The previous owner took it to his local dealership and they replaced the lower seat element.He told me this helped but in a couple weeks it was acting up again.Sometimes it would heat the back heater with no lights on the panel.He took it back to the same dealer and they replaced the door panel switch this time.It works now but you can only turn it on with the back switch.When you push the Bottem switch,you can hear a click under the seat,but no lights will come on the door panel switch.The passenger side works as it should.Does anyone know if there are relays or a brain box under the dr. seat that could cause this problem? Thanks, any insight would be appreciated!