Mercedes Benz repair: MB 83 300SD turbe - Tachometer, 300sd, cable problem

Question
My tachometer is not working and I am unfamiliar with the path of the cable from the back of the insturment panel to whatever it connects to in order to determine if it is a a cable problem or if the gaguge itself is bad.  Can someone assist me?

Answer
The typical issue is the tachometer AMP or sensor.

Tach signal ?
http://www.mercedesshop.com/shopforum/showthread.php?p=402132#post402132

1980 300SD Tachometer question
http://www.mercedesshop.com/shopforum/showthread.php?p=1025701#post1025701

Tachometer Amplifier Schematic?
http://www.mercedesshop.com/shopforum/showthread.php?p=997218#post997218

Tachometer anomalies
http://www.mercedesshop.com/shopforum/showthread.php?p=259699#post259699

Quick Tach Amp Question 85 300TD
http://www.mercedesshop.com/shopforum/showthread.php?p=360233#post360233