The seat heater circuit sounds good, and I do not have heated seats so the circuit is unused.
The fuse board has wiring connected from No 20 fuse (5A) and disappears into the loom. According to my fuse board legend this is for the heated seat circuit.
I am wondering if tails exist under the transmission tunnel ready to connect to the switches installed when heated seats are fitted at the factory ?
Had not thought of the fuse location addition, so thanks for that suggestion. All options are open!
Yes the wiring schematic shows a pair of cable tails with individual bullet connectors in that location. These could be drawn back and re-routed towards rear of dash if unused.