Tach test procedure
 

1985 (early) 944 with inop tach. After reading all the posts on this subject I decided to test my tach this way: Ran a jumper from the coil post (w/green wire) to the pin on the back of the tach that had the green wire. Car ran fine, still no tach. Is this a definitive test showing my tach is no good? If so, anyone have a good tach for sale? (w/mpg gauge and shift arrow, yellow numbers)
Thanks, Chuck

Take a look at the electrical diagrams for the early 944's here on Pelican.

http://www.pelicanparts.com/944/electrical/944_electrical_diagrams.htm

Sometimes it's the grounds.