Hi Ollie, here we go:
Push seat back as far as it will go. Disconect battery v important for safety and for avoiding airbag warning lights if you dislodge the airbag connector. (i left mine for 10 mins to be sure).
On floor next to seat rail nearest the door is a black plastic cover. Pull it up at the front (dashboard end) and you will see the connector blocks underneath. Three connector blocks - yellow block is airbag, purple (I think) block is the seat belt warning light (it is the smallest anyway) and then at the back a big black plastic block. About 5 / 6 wires at the front and one at the back. This is the block that contains the heated seat wires and the electric lumbar support wire.
the wire at the back, black / red coded is the live feed for your electric lumbar support. I cut this off from the connector block as no corresponding wire on the female (car end). On the front wires, two are live. A big fat yellow / red wire which is the live feed to the heated seats from the battery +ve terminal, fused in two places before the seat so nice and safe. Next to it is a black / blue thinner wire, this is the live feed from the heated seat switches, I ignored this wire as comes from the heated seat switches and not great to draw your lumbar current through the seat switches.
I then took a scotchlock "piggy back connector"and opened up the slit a bit to ensure I didn't cut through the big fat yellow / red wire. The Black / red wire I had cut earlier goes into the "blind" channel on the scotchlock, the yellow red wire on the through channel, I crimped the scotchlock shut, did the other seat the same.
The balck cover slides back and pushes down at the front. Reconnected the battery and enjoyed my heated seats and adjusting my lumbar support. Enjoy Cheers John