The smell is probably the ground contact melting on the seat heat module. I had the same issue and the seat heater stopped working after a while. Remove the passenger seat mounting bolts and flip the seat forward. There is a module under the seat with a large white connector. You can remove the module and check the end of it and most likely the connector edge has melted. I ran a secondary wire from the module ground on the module PCB to the edge connector. Still working fine after several years, seats heat and cool with no smoke or smell. Another design flaw.