VSS for nav unit
 

I installed a clarion VRX795BT and clarion NAX970HD nav unit in my 95 BMW 325iS. I found the wire that I thought to be the VSS as per my Bentley manual but the nav unit does not work. It doesn't show the progress in travel. Can someone tell me the correct wire for the VSS in my BMW or direct me to a website that could set me straight? Or maybe give me some other ideas as to what the problem may be? Thanks