My car has the full size spare. I suspect the previous owner put new tires on the car, but only bought 3 tires and used the spare. The wheel that is in my spare well is obviously a used wheel with a worn tire.

Does the full size spare have a TPMS sensor in it? My light comes on but all 5 tires are the proper pressure.

If the spare doesn't have the sensor, any way I can tell externally if the wheel is equipped with one otherwise i have a 25% chance of guessing the correct wheel to have the TPMS switched over to it.