What do you know about the vehicle VSS signal problem? I would think the real solution is to fix the car so the built in speedo works. I understand that may mean something like a new cluster and more cost then the car is worth. It's possible the VSS signal is still good even if the cluster is dead so it's worth investigating.
See this thread for discussion of interfacing to the type sensor used for ABS.
http://ecomodder.com/forum/showthrea...ed-16518.html?
Mike