My heated seat comes on with the high showing. It won't switch to low or off until the key is turned off. There is no heat from the seat.

Is it the module? Fuse?

There are two things to check at the relay from the switch

One is called "input on" from the switch. This enables the relay once the switch is turned on. The other is the temp setting from the switch, you should have off/210 ohms (high)/300 ohms (low).

Then double check that the relay has power and it is functioning properly when commanded by the switch.

From there I would believe the heated elements are either unplugged (doubtful) or there is a broken element inside the seat (common).