I seem to have the exact same problem as yourself 'redborbet'. I've a '93 Corrado with the leather seats taken from a crashed storm but the wiring loom I bought from ebay USA years ago. My wiring loom has the 4 pin plugs on, whereas the seats have 6 pin sockets.
I didn't realise at the time I bought the leather interior that the seats were heated, otherwise would have got all the wiring at the same time.
I've got three slightly different wiring diagrams for the heated seat arrangement and they all seem to point to the 6 pin connectors and the addition of 'seat heater control units' (probably what people are referring to as the relays), not to be confused with the dash mounted heater controls.
One of the wiring diagrams says that the seat heater control units should be located in the right rear seat side panel. I'll have a look to see if there's something there that was fitted as standard (probably nor though).
I'm going to be looking into it a lot more over the weekend so will let you know how I get on. I fear that the wiring looms we have are probably not right though and may even be from a different VW or a an older set up. I'm trying to find a wiring diagram for the wiring looms we have instead of the ones we probably need.
Anyway, investigation continues.......