NEED Help with starter

[gasser]

2018ec300 starter worked perfectly till about 75 hours and was still working perfectly until it hung engaged and burned up the relay/solenoid. I've put on a new starter motor, solenoid, and starter button. I can jumper across the solenoid and the starter turns fine but not even a click when I try a start with the button. That only leaves the diode module and the wiring. How do I check the diode and where can I get one?

 

[gasgasman]

The small red wire at the starter solenoid provides the 12v from the start button.

I would check that circuit next.