non starter weirdness
 

I went for the first ride in a couple of weeks this morning, the bike struggled to start which I put down to a low battery charge. after 20 miles I filled up and it struggled to start again then later not at all.
The last time I got any life out of the starter it turned over a few times then gave up, I heard a whirring electrical noise and the Tachometer went to full scale deflection then back to zero (the engine did not turn over).
The green flag guy put his battery booser on it to no effect, once home I shorted the solenoid terminals the starter worked but there wasn't enough juice left in the battery to start the engine.
The pump always primed and one solenoid under the seat clicked.

Its obvious to me the problem is with the starter solenoid/connections but the FSD on the tachometer has me baffled as to what that indicates - any ideas?

What bike?

Haha yes that would help I suppose,

its a 2000 ST2.

I should think trying to start it pulled the Volts so low that the Tacho lost its reference
Starter Solinoids are often the problem as the busbar and its contacts erode with use. But occasionally it can be the Brushes or the commutator with in the starter motor

or is the battery just past it,what voltage is registering,if it is way to low it simply will not recharge.