Happy to report that I have sorted my Driver side heated seat loom wiring, the wiring loom that came with the car only had 2 wires in the plug but my heated seat (swapped in) plug has 4 wires. Turn out that Toyota only run the 2 missing wires from the centre console up to the driver kick panel, I identified the respective wires (by testing with multimeter while switching the heated element switch On/Off) and extended them to the bottom of my seat, now I have toasty bottom, BUT it takes about 10mins to warm up!!
Earlier i reported that my plug and play passenger heated seat doesn’t work, well I know why now, it takes 10mins… so there was nothing wrong. Embarrassing ..,
But can’t blame me, my Lexus heated seat only needs 2 mins to get toasty.
Summary: if you put a set of heated seat into a GX (or in my case a TX Prado) from a VX, the passenger wiring loom under the seat is plug and play, but you need to run separate wires from the driver side kick panel to extend the switch control 12v to the seat to get it to work!
2 wires to extend, one for HI setting and one for LO, the LO wire also acts as an Earth when put in HI setting, so you need both wires, otherwise you only get a LO setting. Toyota..,
Note: you also need to run a 12v for the Power seat motors but mine was already done when I installed the seats a couple of years ago.