@David, Thanks a lot - this is precisely the type of information I was looking for!
Looks like I
could do it, but I'd better not. (I hate wrecking 100s of £s of equipment!) I think I'd better let this young, electronics whizz I know get his soldering iron out.
Thinking about it, though, as interesting as Oil Pressure and Temperature are, I think I'd value MPH a bit more. (Though this could be a bit incriminating
)