The POS battery cable runs to a device with two huge post terminals on it. That is your solenoid.
The other big post should have another large cable and that goes to the starter motor.
To test if your start motor is working and your battery good enough to operate the motor, you can bridge the two posts with a thick piece of metal. Pliers handles will do the job. But, expect sparks, and a mark on the handles where it got hot making/breaking the circuit.
Also note that this bypasses all safeties, so if the bike is in gear and the rear wheel on the ground, it can lurch forward. Won't matter if the key is on or not.
If the motor didn't spin, either the starter motor is bad, or your battery is flat.
If it does spin, then test the solenoid for operation.
There are two small wires on the solenoid. One is Yellow/red the other is Green/red. Disconnect them and jumper each to a battery post. The battery power should activate the solenoid and the stater motor spin. If so, the solenoid is good and you can move on to bike wiring issues. If not, the solenoid has failed, and needs replacement or a rebuild.
If solenoid has proven good. Then leave the Grn/red jumper on the battery NEG terminal, reconnect the Yel/red, key switch on, and press starter button. The starter should engage. If so, then the Grn/red circuit is suspect. If not, then the power distribution is suspect.
You can reverse roles, too. instead of reconnecting the yel/red to the wire harness. Connect the Grn/red to the bike's harness mate terminal. Then each time you connect the solenoids Yel/red to the Battery POS terminal the starter should engage. If not, the Grn/red circuit is suspect. If the starter does work then the yel/red is suspect.
The troubleshooting branches are now spread in several directions. I don't want to describe them all now. Report your findings and we can proceed to find root cause of failure on a more direct investigation path.
Cheers,
