the fact that the switches are illuminated it means that power gets to them...so, first step: Rave > electrical library > connector views > C0969, u'll see C0971 near him, there is no pic about the connector face but u can identify the pins by the colour of the wire in the table near the pic. Put voltmeter (-) on 971 pin 3(O wire) and + on 969 pin 1(K wire) with switch on there must be 12V there... if it is then one of the heater elements(or the contact of it) is burnt... serieal circuit. This procedure is the same for both seats. If no power there we'll go further...
u have the wire colour codes in electrical library - introduction ... good luck