[tepetit53]

Had that problem on an '80 CM400A I just picked up. Means that the starter solenoid is drawing current but not engaging. A sharp rap on the solenoid with the but end of a screwdriver freed the thing up.
You also need a better set of schematics than that. PM sent.

 

[tepetit53]

According to the schematics, these are electrically correct. The schematic does show a mechanical splice for the black wires coming off the red plug. The print also shows two green coming from the plug. Doesn't show a splice, but electrically correct. The splices aren't kludges so more than likely correct.
One of the green conductors should go to the starter switch and the other to the headlight via a connector. One of the Black conductors should go to the starter switch and the other to the front brake light switch.

 

[tepetit53]

Check continuity on the solenoid where the red/yellow wire and the green/red wire are connected.
Should be very low resistance.
Still think the solenoid is stuck.
If you can connect directly to the starter motor and get it to go, then it means the solenoid isn't engaging.

 

[tepetit53]

Something a bit kerflukey here. Originally you said that when you pressed the starter button, the lights dimmed and the starter motor did nothing. This indicates a heavy current draw (the solenoid coil). Nothing happened re: starter motor. Indicates that the solenoid did not engage providing high current to the starter motor. If your starter switch contacts measure > 1 megohm, there is no way the lights would have dimmed. Also, it indicates that the grounds could not have been interrupted.

Why do you now think that the solenoid is toast? Did it heat up? Did you hear the armature move?

The solenoid doesn't care what the polarity is. Nor would I have connected it directly to a battery for any length of time. It is designed for short powered intervals.

If you did not experience excessive heating, then the armature is more than likely stuck.

 

[tepetit53]

You're probably right. If your suspicions are correct, then measure the resistance between the coil terminations. It should be open.
When you shorted the bolts, you did what the solenoid was supposed to do.
The good news is that the starter motor works!