As I understand it some used the switch for the horn and others use it for the Hi-beams.
Since it's a momentary switch a "latching" relay is used to flip between Hi-Lo.
There's a thread about this in the Kirkham section I think. As I recall it's a VW relay as well as the turn signal switch.
Found it:
http://www.kirkhammotorsports.com/ma...merrelay.shtml