Bouncing Tachs

[Vihurah]

So during this rainy spell on the midatlantic I noticed my tach has stopped functioning quite right. It's an EI R-1 Digital Tach i got with the plane, and I'm not really sure what to make of it.
My mechanic told me to check if the wire is a set right, and it doesn't seem loose but it's kind of old looking. Main concern is that it's not the tach itself. Any ideas?

 

[Ryan Klems]

The wire in your picture looks like a thermocouple wire for a CHT or EGT probe probably. The R-1 tach gets its signals from the magneto switch (assuming installed as per the manual). It attaches to the p-lead terminals on the back of the ignition switch, through a resistor. If the connections to the back of the ignition switch are loose, or the crimp connections between the resistor and the leads to the instrument are bad, it could read wonky. There is also a circular connector for the wiring harness at the back of the R-1, which could potentially be loose as well, though I'd expect the instrument to be power cycling as well if that were loose.