My GLi has them (although it says Plaza on the V5), once I put the Senny seats in I was able to fit the switches in the centre console and hey ho - heated seats, work a treat too...

My GL had the wires under the carpet too, when i got a CDX interior off Murph (Cheers mate) with heated seats, iv plugged them in, but dont know if they work as i aintdone the switches yet, but from what i hear from other people i hear they do all work.
I think vx fitted every carlton with a loom for all the extras, its just if you didnt have the extras, they just didnt plug in the appliance, but all the wiring is all there, even the sunroof iirc, if you have the manual, the earthing etc is under the manual toggle ready to be fitted with the elec motor, i may be wrong.....haha
my senny has manual windows being ex-plod, but there is wiring there behind the doorcard for a elec motor to be fitted for the elec windows.. which is something i think i may have to do now, the ever so slightly lightweight of the manuals 'aint' outswaying the hassel of them.. ha ha