Tach randomly stopped working

[Tooch]

So I fired up my wife's bike. The tach jumped around a bit then dropped to 0. I haven't started it in a few days but it does have a new battery. I figured it was just low voltage, but it didn't come back after a few minutes, so I hooked it up to a tender for a while. Retired it and still nothing. I did a search on here and apparently a boogered up tach isn't all that uncommon. Unfortunately I do admit I have trouble reading a wiring diagram. Can someone show me where the tach gets it's feed from the engine and where it's ground is? I'd like to rule out electrical before I start looking for a new tach...

Thanks!

[DannoXYZ]

Two possible causes of non-operational tach.

1. Stiction in needle-shaft. It spins in brass-bushing and can get bound up. Drip some light oil onto bushing and rotate needle a little to work it in

2. Broken wire between tach and left coil (where tach gets signal). Use oscilloscope at coil and then at tach to verify that exact same signal arrives at tach. Should look something like this, logic high with periodic grounds to fire coil.

[Tooch]

Thanks for the reply! As that looks like my old TI-81 calculator in 7th grade, and I hated math, I'll check the wire going to the coil first haha

It sounds as if the gauge cluster is easy to manipulate apart?

[DannoXYZ]

Yeah, just remove upper fairing and all dash wires can be accessed from underneath cluster.

Note, unless you're Superman and can see electrons flowing, how will you know if wire is good or not? A lot of problems come from wires broken underneath insulation.

[Ralgha]

You could test the wire continuity with a multimeter, way cheaper than a scope. Won't help you beyond that though, if the wire isn't broken and it still doesn't work then you'll need a scope to see the signal.

[InvisiBill]

The gauge itself uses the same brown accessory wire and common black/yellow wire as the rest of the dash for power and ground respectively. As DannoXYZ said, the tach signal is just a fork of the black wire running from the igniter to the coil. Assuming your black wire is good, and the coil is working properly (which means the igniter and main black wire are working properly), that pretty much narrows it down to the gauge - either something wrong with the gauge itself or a bad connection to it.