Start with the wire to the sensor. If an original set up the temp sensor is a single wire connection at the front of the thermostat housing. It is common for the wire to break at the crimped connector. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Kk Al
Sent: Saturday, September 5, 2015 5:09 PM
To: vanagon@GERRY.VANAGON.COM
Subject: 87 Syncro no temp gauge

We noticed today that the temp needle didn't budge at all. The radiator is still getting warm, the heaters still work and the coolant level is fine.
  The red warning light in the temp gauge  flashes a few times when we turn on the ignition, then remains off.

How do we track this problem down?

Thank you in advance