I had a blackout in the past which I fully changed the flipper mechanism.

I do not remember exactly, but this switch might be with the EOS on the right flipper, under the playfield.
Whether it is on the flipper button or the EOS, have you checked the contact of the lane change switch blades with DMM ? Flipper off, actuating the button, or the coil if at the EOS.

The lane change switch goes to the CPU on the switch matrix connector. Maybe you can check the continuity of the wire between the switch and the connector on the CPU (see colours, only one of the wires)
Also there should be +5Vdc going to this switch

As for rebuilding the flippers, I rebuild all my Williams Solid State games the same way -- with all new parts:
-mof

Part list:
https://pinside.com/pinball/forum/topic/system-11-club/page/6#post-1019065

To learn all the ins and outs:
https://pinside.com/pinball/forum/topic/vids-guide-to-upgradingrebuilding-flippers

Rebuild your entire flipper mechs.

https://pinside.com/pinball/forum/topic/vids-guide-to-upgradingrebuilding-flippers

Post a CLEAR, WELL LIT picture of the lane change switch and diode.

Make sure we can see the colors of the wiring.

What a mess that switch is.

Looks like you are missing the diode altogether.

Unsolder the GN with BL stripe wire and add in your diode. The banded side of the diode should attach to the green wire, the unbanded, the switch leaf.

Order a new switch next time you order parts - that one is crap.