As one who has in the past repaired far too many butchered wiring harnesses, here's how to bypass/eliminate the K1100 sidestand engine kill switch either temporarily or permanently, without altering or damaging the wiring harness. Get BMW part P/N 61-12-1-459-998, called a "contact ring".
It's actually a jumper encased in a specially designed connector that plugs into the harness, substituting for the sidestand cutout switch. It enables the engine to run while the bike is on the sidestand for diagnosis/repair. Makes defeating the sidestand switch a one minute operation, and it's completely reversible.
I keep one on the bike, zip-tied to the regular harness wire, just in case my sidestand switch fails on the road. Just remove the right side cover, unplug the sidestand switch, plug in the jumper plug, replace the side cover, start the bike, resume your ride. At about $12,the plug may seem a little pricey, but it's worth the price in convenience and wiring harness damage avoidance.
The question has been asked whether it will fit oilheads. I haven't checked, but a simple way to find out would be to park a K-bike and an oilhead side-by-side, unplug their sidestand cutout switch connectors and compare. Since the jumper plug simply replaces the part of the connector to which the sidestand switch is wired, if the connectors are identical, then the jumper plug fits both bikes.
A word of caution: Because this plug is normally for "Dealers only", so when you order it, don't you talk too much about what its purpose is or why you want it. If you do you may set off the dealer's liability/litigation alarms and encounter resistance/refusal to sell it to you. Better just find a not-too-knowledgeable parts counter person, and simply order it by the above number.