Most likely a foil problem, probably at the 14 pin connector.  This is where most failures occur, the copper trace cracks going into the connector. I've soldered fine wire across breaks several times, but finally gave up and got a foil replacement kit: 
https://www.vanagon.org/products/instrument-cluster-foil-repair-kit

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Steven Shelton
Sent: Wednesday, August 23, 2017 4:17 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Intermittent Tach

We just got back from our eclipse trip. We went from Atlanta to Cumberland Mountain State Park near Crossville, Tn., about 170 miles away.
Surprisingly, there is only one item on my post-trip punch list.

At times on the trip I'd look at the tachometer and it would be reading zero. All other instruments were OK. I'd look at it again later and it would read normally. One time I saw it suddenly jump from zero to the correct RPM. My first guess is that the connection at the coil was loose or corroded. I looked at all the connections (I don't know which one is for the coil) and they were tight. I cleaned them all anyway and bent some a little that looked like they could be tighter.

I may not notice the tach just driving around town and would rather not wait until we go on another long trip to  see if I fixed the problem. Is there something else I could look at?

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