I repaired the switches that control the heated seats, they now illuminate when in the Hi and Low positions.
In that case, don't worry about the fuses and the relay. Looking at the wiring diagram of the seat heater system that I attached earlier, we see that when either the left or right seat heater switch is turned on, the bulb in the switch is powered from the same connection as the heater. For example, on the left side switch, when in the LO position, the power coming from the relay to terminal 5 of connector R43 goes through the switch to terminal 6 (to the heater) of R43, and also to the top end of the bulb. The bottom of the bulb, at terminal 3, goes to ground. This tells us that if the bulb lights up in the LO position, there is power coming from the relay to the switch. The same analysis applies in the HI position. So the relay etc must be okay.
If this is the case, then if the heaters don't warm up, it's far more likely that either the connector to the heater is loose/off, or the heater is faulty (open-circuit.) This will require measurement at the seat heater connector. As cardoc suggested, check for voltage at the harness connector R44, and for loose connections to the switches. In addition, or perhaps before doing those measurements, check the seat heater itself. The seat heater can be checked for continuity (low resistance) between terminal 4 and terminal 1 of the heater connector (e.g. R44 on the left side seat), and between terminal 3 and terminals 4 and 1.
Keep in mind that even in the HI position, the seat might not be warm enough to check with a hand. However, if you sit on it for a while, it should be noticeable.