Tach problems(erratic readings) help

[Fr. Frank]

Quite a few people have told me to move the selector switch on the back of the tach back and forth several times.They claim it's common to get corrosion on the internal contacts at this switch point which causes erratic readings.
I only hope it's that simple.I'll llet you know what I find.

Use a good electrical contact cleaner just before trying this. If it's a mild film of corrosion, the contact cleaner will break up the surface of the corrosion, and then leave a protective lubricant film behind. I use Radio Shack's "Control/Contact Cleaner and Lubricant", item #64-4315, on electrical cable connectors, switches, potentiometers, etcetera. I then spray the outside with Fluid Film to provide a light moisture/salt barrier.

If you don't use a cleaner, you may just scratch a temporary connection through the corrosion, that will then fail again fairly soon.