Hi Mate,

I have done this for my S1 replica cabby.
It is al lot (and I mean a LOT!) of work! I have made alle the switches and auxilary warning module into the S2 loom. Biggest problem is that Mk3 switches are "hardwired" and Mk4 switches use relays for switching things. Mk3 switches have a common +12v for switching, and the MK4 ones use common +12v and common ground, depending on relay state. This makes the internal wiring in a switch different, so extra relays are required. I had to place severel additional relays for it to work....
Unless you are very good with electrical work, I would advise against it.....