[Sergio]

The side of the diode with the band (cathode) always goes towards the positive activation wire when used as a flyback diode.

The issue I see there is that you have the small connectors under the main lug, that is a big problem.

On those type of Solenoids the main cable goes in direct contact with the large metal surface, no other cables or washers go under the cable lug.

Any other wires go on top of the main cable.

The same applies to battery posts.