New Fabia/Roomster GALA wire?

[_bomber_]

In order to fit my Blaupunkt SatNav unit, I had the standard Skoda stereo (the "Dance" unit) removed and the Skoda ISO converter cable fitted (this is a standard Skoda accessory that is common to the Fabia and Roomster). I thought this would let me just plug in the Blaupunkt unit as that has standard ISO wiring, but on inspection I found that only half of the ISO pins are actually wired in the adaptor.
Since the SatNav won't work without a GALA speed pulse connection I need to know where to get one from. Now I believe the Dance unit has speed-sensitive volume, which implies that the speed pulse wire is there somewhere, but does anyone know what colour it is?
Failing this, there must be a speed pulse supplied to the instrument panel, but again does anyone know what colour, and where it can be most easily accessed?

Thanks in advance,

Mark