When measuring voltage at starter-solenoid terminal B, if you don't have voltage, stop, you've found problem: B and M connections are reversed.
1. Disconnect battery +positive cable
2. Disconnect cable at B terminal
3. Disconnect cable at M terminal
4. Don't let go of it and immediately attach to B terminal
5. Attach remaining cable to M terminal
6. Connect battery +positive cable
Go back and repeat tests from step #1 above.
Here's similar case where guy refused to believe that his cables were on solenoid backwards:
https://www.ninjette.org/forums/showthread.php?t=345904
Thing to note is that terminals B and M at starter-solenoid are not identical and interchangeable. Just because you can connect them with needle-nose pliers and get starter-motor to run, does not mean you can connect them any which way.
Battery +positive cable
must be attached to
B-terminal. Starter-
motor
must be connected to
M-terminal. There's absolutely zero way around this with any other configuration that'll work. That's because it's
B-terminal that sends power through 30-amp main-fuse to ignition-switch, which then powers rest of bike: lights, ignition-coils, IC-ignition, start-button, starter-relay, starter-solenoid, starter-motor.