FYIActually, I'm interested in this too. I'm looking to fit an on/off switch there to kill the headlight and run a pair of fog lights instead. Commuting out of Wollongong in the early hours can get very foggy up the top of the hill and I need to do something. If I can buy the switch from Husky and run the power for the headlight lo-hi beam switch through it, it seems like it would make a neat and simple on-off switch.
The way BMW manage turning off the headlight and other items when the starter is engaged is rather simple and a little tricky, they run the earth return of the "Load Relief Relay" through the starter motor, it is a very low impedance as you could imagine. Perhaps similar could be done with the headlight relay on the Terra