I am trying to figure out whether the 82 500SL has a speedometer cable or if it is an electronic pickup. When I removed the cluster & looked at the back, the raised white ring with silver plug in the middle had NO cable attached to it. The speedometer, though, reads about 50% too fast i.e. I'm driving 40, it says 60. It's a euro but the main dial reads in MPH. If it was supposed to have a cable and it is detached, why is the instrument giving a reading at all? If the cable is missing, where do I attach the new one (that I will purchase)?