I have a 94 Q45 without heated seats. Would like to convert to heated seats. Does anyone know if the heating elements are in all the seats or not? Would seem to be less expensive to manufacture all the seats the same. Thought that maybe everything is there and would just need a switch and to connect everything.

In my experience Nissan didn't do things that way. Even wiring harnesses that you'd think would be easier/cheaper to standardize were made with just what was needed for the most part.

Both my G50s have heated seats and TCS (active models). You might start with removing the little 'coin tray' just fwd of the console storage box, and see if there are two unused connectors (one will be a 12-pin, but with 3 'missing' wires, the other would be a 10-pin with one 'missing' wire. That doesn't prove the elements are in your seats, but it's probably easier than pulling the trim and cushions on the seats.