Just did this over the W/E. Put in four relays so that I could turn off each headlight separately, '06 Girly.
Relays are common Bosch, lined up in-between the headlights, three on a bracket from an 80's BMW, the other tie-wrapped on top.
Terminal strips were used, power window items from inner door, Merc W123 (240D - 300D, 1976-1985). Also used the main terminal buss from same car, under Tigger's seat.
Diodes necessary on each trigger positive, due to backfeed sticking the relays.
10ga wire from main buss to headlight relays assures plenty of power.
The ability to kill one or both headlights allows for more power when I am using heated clothing/grips/seat. There are pilot lamps in each unit, so am quasi-legal-ish on the headlight laws here (on all the time).
Switches are tiny on-off units from remote starter kits sold at my place of employ. They just throw them out. Placed them just above grip heat switch.
Pics impossible, due to my embarrasment over wiring colour. Wiring diagram possible, if any interest.
Why did I post?? To let you know that this is possible, and fair cheap - I used almost all components from the breakers. BMWs are too expensive to repair, so my local breaker is full of them. Mercs the same, though they use proprietary relays that cannot be sourced easily if you are stuck in East Jesus Lost His Shoes Here.
Cosmo