stereo sat nav install

hey guys and girls, ran this past local dealers and they were so confused,just wished me luck and showed me the door, i have an intergrated stereo sat nav system made by blaupunkt, in the germans quest for world supremacy the system has to be wired to the din/iso sockets, easy fix there, but also has to be wired to the reverse lamps, and speedo drive, called gala sensor in the manual, to allow for correct speed and positioning, well annoying i know but am determined to fit it, i know that 2000 on v40s had these fitted into the stereo area for the later sat nav installs but mines a 1998, anybody tell me where they hide dashboard area so i dont have to run loads of wires through the car, all help appreciated with wire colours too cheers rob