Neptune 4 printhead mounted filament Sensor for reverse bowden

Housing that repackages the N4 filament runout sensor to sit on top of the print head, uses the PCB, spring, the small baring and its pin.  Will need to use 2 M2 bolt/screws for the top lid (I took 2 of the little black ones from the side of the print head) and an M3 bolt/screw to attach the sensor to the print head.
Will also need to extend the existing 3pin JST XH cable by 40cm to run it along the print head cable.(measured on my N4 Max, other printers may very)
Alternatively, if using a non stock bed level sensor, e.g. beacon/cartographer, a 20cm 3pin JST ZH to XH cable can be used to connect the sensor to the probe connector on the printhead board, unplug the existing "Filament detector" cable from the mainboard and swap it for the "proximity switch" cable.

I'd recommend smoothing off the sliding surface's on the housing and slider with 600/800 grit sandpaper, run a 2mm drill bit through the filament path and to douse the inside with dry PTFE lube.

Red parts need gluing on.

^ Fit the “6mm bowden tube connector boss” to the ”housing top” and secure with CA glue

^ part: “bracket (tab)” glues to the back corner of existing 5015 fan shrouds

^ for stock shrouds bolt “bracket (no tab)” to the print head then glue it and the housing together