Thank you very much for that link. I just bought it (with the relevant change from pounds to dollars). Here's the shorter form of that link:
This adapter cable fits exactly to the existing original plug of the S 1000 R/RR and XR and is divided into three wires: - positive line - not required This means that additional devices can be easily connected without having to cut apart the...
www.ebay.co.uk
BTW:
1) I found a few of them, but they all seem to come from this one seller in Germany, WhileLightsForBikes:
https://www.ebay.com/str/whitelightsledlightsforbikes
2) So there are positive and ground wires, and a third wire you just ignore, correct?
When things warm up (outside and in my garage) in the spring, I'll take the handlebar covers off my '22 C 400 GT -- something I've done once before, when doing some through-the-dash farkling -- and look for the matching OEM plug. I didn't notice it before, but I wasn't looking for anything, either. Then, assuming I find it, and assuming that that plug I just ordered matches up, I'll put a voltmeter on the wires of that ebay plug and confirm what's going on.
If all of this checks out, I plan to use this to power some Skene fender-bolt-mounted LEDs, the conspicuity kind, not driving lights (I haven't ridden at night in years) that I bought a couple of months ago:
https://skenelights.com/photon-booster-led-modules-pair.html
Thanks again for pointing out the proper plug.