71 Mach tach stopped working

The tach on my 71 Mach has suddenly stopped working.  It worked fine uo until a couple days ago.   I had to get the car hauled to a tranny shop (they had to pull the tranny and replace the flex plate).   On the way home, I noticed it wasn't working.  I suppose there's something the shop could have done,  but don't know for sure. 

Anyway, I checked the connections in the engine compartment,  looks OK.  Is there a fuse that might affect it?  What else and how can I perform any other checks?

No fuses. Since the car still runs, there are only two ways that can happen: the shop removed the dash cluster and bypassed the tach (unlikely), or the tach gauge guts have failed, but not the input transformer.

Mine stops working every now and then, especially after the car hasn't run for a while.  I just tap on the top of the dashboard above the tach and it jumps back to life. Not a technical fix but it does continue to work after that for a long period of time.  My other Mach 1 does not ever have that issue.