Ummm, no offense, but you've just helped to reinforce my point. That point being that leaving the key in the ignition with the power still on is still more of a "operator head space" as we say in the tech world. (no offense meant, I have moments like that as well, we all do
)
It's kinda like how I've had to get on my roommate's case about using the parking brake on my car. He has a manual trans car and has to use his parking brake all the time when parking his car. My car is automatic but with all the controls in the same spots as his car and he kept forgetting the parking brake on my car for some reason. You would think that if you're used to using the parking brake EVERY TIME you drive your own car that it would be almost automatic to use it regardless, especially when all the controls are in the same spots.
Anyway, back on topic. Have you gotten the tach working again? Was it simply the battery or something more?