Robbie
I just looked at my car and there are 3 wires going into the inertia switch.
The 2 larger ones are white with purple tracer , the smaller one is grey. Looks like your friend has the same wiring as I do.
As far as I know the fuse boxes changed a lot as more electronics were added to the car, and some owners modified them for their own needs , so that is not altogether unusual.
