There are differences in switch clusters between the single spark, dual spark and the G650 models.
The information here is oriented to the F Series but much of it applies to the other models as well.
There are a few issues with the switch clusters which cause problems and a few repairs which can be made to avoid the costs of complete switch cluster replacement.
The information here is a collection of repairs with contributions from a number of people.
BMW run the full power of the headlight through the switch and it is common for the switch to overheat and damage the contacts. A solution is to run the headlight through a relay which also reduces load through the load relief relay.
The original switch repair thread is at F650.com and well worth reading.
A modified version of the headlight switch repair thread is in this repair pdf
The power of the headlight runs through the switch, the contacts get dirty and can fuse together or fail to operate. Headlight relays resolve the issue.
Open the LHS switch cluster and clean any dirt from the switch.
Use a small folded piece of 600 grade wet and dry sandpaper to clean and polish the contacts.
The indicator switch is packed with grease. The grease dries and dirt and brass from the contacts turn the grease conductive. Wet weather can highlight the problem. When LED indicators are fitted they can flash dimly.
The switch should be cleaned and repacked with grease periodically.
The wiring on these switches is more exposed and can break off at the solder points. Cable tie the wiring to the switch mount.
After market switches can be used as replacements and the switches mounted closer to the clusters.
The ABS switch is a normally open momentary action switch.
The kill and starter switch can collect dirt and become intermittent in operation.
The switches should be cleaned and repacked with grease periodically.
Also see the wiring repairs page, the wiring can fracture inside the loom.
Kill Switch. The kill switch wiring causes some confusion with owners. The kill switch supplies power to the operating coil of the Motronic Relay which powers the BMSC/BMS-E so poor contacts or damaged wiring can cause loss of power to the BMS. It is different to kill switch operation on many dirt bikes which are a short to earth operation.
Starter Button. The starter button power is from the same wire as the kill switch power.