Well done Rob,even though I have worked in the trade from 1972 till now I am not really willing to tackle electrics as it was never needed,we just farmed it out to a sparky.
Problem now is that every mortal thing on cars goes through some ecu or controller so you need a laptop to talk to the car and the brain of Einstien just to turn off service lights,VAG in their wisdom have added a new protocol to their systems and even the dealers tell the customer "the light may come back on ". So I have had to learn the hard way,and £3500 lighter in the pocket for the hardware.
All credit to you for even trying, Need is the master of invention.
Would be good if the more electrically wise amongst the forum could maybe sort a beginners guide to electrickery