You have lost all seat function, so it is probably the hot wire to the switch that has broken due to flexing from opening and closing the door over the years. remove the switch and take a voltmeter to the plug connections. This will tell you if the switch or it's power supply is the culprit. By the way, the switches can be cleaned if one function has quit. Take a section of a newspaper, fold all 4 edges up and tape them to form a tray. CAREFULLY use a very small screwdriver to separate the halves of the switch. Be gentle and pry only the clips open. Little balls and springs will fall out everywhere, hence the tray made from paper. Clean all the contacts, then put a small amout of dielectric grease on each. A little playing will tell you where everthing goes to put the switch back together. The alternative is an expensive replacement.