Problem with Tachometer on 300SD
 

I've got a tachometer problem on my '83 300SD and need some help to determine what part or parts I need to fix it. Originally, I thought it might be the tach sending unit module located in the screw-top casing over the driver's side wheel well. I put another one in and still no tach signal. I then traced the wiring coming off the tach sending unit module looking for some type of pickup and came up with about three feet of wire that seems to have detached from something, perhaps due to vibration. So, is it possible to purchase just the wire lead between these points and, perhaps more importantly, how does it connect? Does it just plug in somewhere? What is the part or parts that I need called? On a similar note, my cruise control isn't working. Might the lack of RPM input from the broken wire be the culprit? It seems feasible but I don't know how they might be related on this car. It would make my day to be able to fix two problems with only one part.