Starters, like all electrical devices need two conductors, a Positive/hot wire from the starter switch, and a ground wire to the chassis or back to the battery. Sometimes, the ground may be internal to the starter and thus there is only a single terminal or wire connector for a Positive wire from the starter switch.
NOTE: The first step is to make sure that the transmission is in NEUTRAL!!!!! Also, leave the ignition switch off.
On most motorcycles there is usually a wiring harness connector at the starter. I disconnect that harness [or if there is only a single wire to a terminal on the starter then disconnect it], and test the starter by connecting a wire from the ground wire [usually black] in the starter connector to the frame of the cycle, or to the battery negative terminal. This step is not necessary IF the starter is grounded internally.
I then connect another wire to the hot wire [or terminal] on the starter or connector [Or the terminal on the starter if it is internally grounded.
I then just very monetarily touch the other end of that wire to the Positive terminal of the battery.
IF the starter cranks the engine, it is probably good. Sometimes, IF the brushes in the starter are worn out [or "glommed-up" with Carbon dust or other debris] the starter may try to crank the engine, but unsuccessfully.
If the starter does not do anything, or tries but can't crank the engine, then it may be worn out and needs an overhaul or replacement.
You know the starter is going bad when you have a dragging starter.
Remove the starter and have it bench tested.
Remove starter and bench test it for operation and current draw
You need to remove the starter and look at the teeth on both parts.
Remove the battery and take it to an auto parts store for testing. They can tell you if it is bad. If it is good, then remove the starter and do the same thing.
If the starter does not turn then it could either be bad or not getting power. If a volt meter can not be used to determine that voltage is present, then the starter can be pulled and taken to be tested.
Remove it and have it bench tested.
jump the starter solnoid, if it will crank , turn key on and jump again, if it starts then key switch is ok it would be the starter solnoid that's bad,
If a starter relay or solenoid is bad, usually you will only hear a single click when you turn the key to start the engine.
Remove the starter and inspect the ring gear on the flywheel.
Good power all the way to the starter, 12 volts at solenoid/start circuit wire when key engaged, but no click or starter engage
First, turn on the headlights. Now, have someone watch them as you try to start the car; do they get dim? If so, the battery is in need of a charge; If not, you need to check your connections at the starter. You may have a bad starter, starter solenoid, or connection.