I had this happen on the drivers seat. I found one of the two wires, that should have connected to the thermostat, hanging loose under the drivers seat. I thought the wire was a little on the short side so I spliced in a couple of extra inches (soldered the connection for good measure) before putting a new blade connector on it. I dropped in a bit of extra electrical tape over the connectors and onto the wire so that the wire is less likely to flex at the connector when I get in and out of the seat.

I did have a bit of an awkward time getting the thermostat down out of the seat foam. The thermostat is a small metal cylinder surrounded by a large white disk with some prongs on the bottom. The exercise was easy enough. Hope it's just the thermostat or a bad connection. Good luck.