Within the last month or so, I've been seeing some weird behavior from my tach...

Sometimes, it works fine, but that's been becoming pretty rare...

Sometimes, it will read somewhere between 1/3 and 1/2 of what it should read. When it's doing this, it will definitely stay at that exact-but-undetermined fraction of the real RPM's. It doesn't seem to vary while it's happening, but it DOES seem to vary from one driving session to the next.

This morning, however, the needle barely moved...at idle, the needle was resting on the peg, and at approximately 2500rpm, the needle barely raised off the peg about 1/8". This afternoon, though, the tach seemed to be working fine.

Any thoughts? Does this indicate a problem with the tach itself, or should I be looking elsewhere? There's no other apparent problems.