The end-stop is not defective. When it goes into the end-stop it won't let me engage it in or back out again. I have to use M84 to deactivate the motors, and drag it out of the end-stop. Once it's out - the Y-axis responds again. This used to be a problem on the X-axis as well - until I changed the Bed Left to 23.9 in Offset value. Now the X-axis can engage all the way into the end-stop, and continue all the way over to its limitation at 298mm. This is the way I would like it to behave.

According to user manual and instruction video, everything is correctly wired. I might have assembled the engine assembly on the Y-axis the opposite way of what the user manual says. I could try to change it over tomorrow, and see if it makes any difference. My thought was that this should be possible to climb around in the software.

The firmware was pre-configured. A .COM launcher of sorts I installed for it to function against the printer. I configured the software according to the user manual, but modified it to meet the specs of my printer. I left these quite early though, as I discovered other things that worked better, thus getting the X-axis working.

Everything is properly connected. The only thing that could be re-wired is moving the end-stop from MIN-state, to MAX-state. I tried doing this on the Y axis, as the end-stop might be at the opposite side given I have assembled it incorrectly. This was without luck, as it only stops the Y-axis from moving in the decreasing direction.

Thank you again for all help!