Craig (now fellow ADV'r ACEWELL UK) has been MOST helpful in explaining the internal wiring of the units that I have used. I sent an email to their general "technical advice" address the other morning (east coast US time) and within hours had a concise, personal and well-thought-out response to my question. SUPER! Almost as an afterthought, I sent him a link to this thread, which Craig obviously read, and then responded to me, personally, again...
Cannot say enough good things about the effort to provide service!!
I posted the Acewell UK link up ^ there somewhere, but for all who are interested, here it is again:
Acewell UK speedometers
Airhead boxer sensor is under "speed sensors-cable drive" and is the Ace-S11
on the left side of the homepage.