Blaupunkt Autosound-Speed Sensitive Vol?

I'm in the process of installing a Blaupunkt Casablanca CD51 on my motorcycle.  Despite the cartoons which Blaupunkt refers to as "Installation Instructions", I've figured it all out since it is pretty straightforward.

Conveniently, Blaupunkt totally ignores the presence of the "Autosound" lead in their diagram. (Autosound, a.k.a. GALA, is the feature which automatically lowers or raises the volume based on the vehicle speed.) I know that my motorcycle uses some sort of electrical impulse from the rear wheel for the speedmeter. (I tore down the rear end do to some maintenance so I know it isn't mechanical.)

So, I know which wire from the head unit is used for the autosound feature and that I have an electrical, not mechanical, speedometer.  So, how do I hook this baby up?  I assume I either spice it into the speedo cable (which scares me a little) or put some sort of inductive coil around the speedo cable.  But, then again, I'm just guessing.

Any advice from someone who's done this successfully before would be greatly appreciated.

On a side note, I'm also thinking about putting this head unit into my convertible if I end up liking it. The convertible, on the other hand, has a mechincal speedometer. I'm also curious as to how I might hook this feature up in that situation but it is of secondary importance right now.

I think they intend for that wire to be hooked up to the VSS wire that most automobiles have.  Since you said you know your bike's speedometer is electrical, that most likely means there's a VSS wire somewhere.  Now as to where you might find that wire on your bike or what type of meter reading you'd get, I really don't know.

You might want to also try posting in the Cruise Controls forum as the "regulars" there know a lot more about VSS's than I do