I installed a Euro switch on my R100GS so that I can turn off the headlight last year. I wanted to do this since I was concerned about saving power while off road and traveling at low speeds. It's also handy in the event of electrical charging problems like a rotor failure. The draw back to the Euro switch is that it costs $70, but it looks much nicer than a non stock toggle switch sticking out from somewhere.
Later, I heard from Noemi Berry and Doug Ruth that there was a simple mod that one can do to the R80G/S ignition switch to make it double as a euro switch. Looking at the schematics, sure enough it's very simple.
The US spec ignition switch has three positions off, park, and on. There are four wires that go to the ignition switch,
Moving and joining the green wire which is currently on terminal labeled 15 on the ignition switch to where the grey wire is, which in on terminal labeled 58, will allow the engine to run when the ignition switch is in either "park" or "on" position. The headlight is only on when the ignition switch is in the "on" position. This effectively gives one the ability to turn off and on the headlight while the engine is running.... very similar to the Euroswitch, with no additional cost, or cosmetic change.
While I did perform this modification on an '81 R80G/S, glancing at the schematics for other bikes, it appears that this would work for most other BMW R bikes. Check the schematics to be sure. The Haynes manual has excellent schematics for the various bikes.
An additional note, I believe it's illegal to drive a motorcycle on public roads without a headlight on for most, if not all states in the US.
Dave Thompson
Champaign IL
'82 R65LS '92 R100GS '81 R80G/S
davet@spyglass.com (http://www.spyglass.com/~davet)