So, I have finally given up on resistors. Searching the US SVT forums revealed that common thinking over there is that it is a resistor and capacitor in series that's required. that would tie in with the error message I'm getting which is "capacitance out of range" when i put in a resistor on it's own.

I'm pretty much outside the little electronics I leaned at school with this so I'm probably going to give up and try plan B. that, is to buy an airbag module from a Mk1 RS which should be set up without seat airbags and swap mine out for it.

I have one on it's way, so we'll see how that goes.....