I added a lockable diff axle to my Scania R620 but needed a way to mount a servo for actuation and a cable stop to manage the cable housing on the servo end.
My guess is that this will work with most Euro COE semi's and maybe just about any semi. Holes may need to be drilled in the top of the frame rails to mount the top plate.
This replaces the fifth wheel release arm plate and adds a mount that screws to the bottom of the plate, attaches to one side of the servo and includes the cable stop. The servo mount attaches to the top plate and the frame rail. Where it attaches to the frame rail a hole will need to be drilled in the rail and tapped for a standard 3mm Tamiya screw. I actually haven't attached that side of the servo mount to the frame rail yet and it seems to work fine, so it may be optional.
The cable stop / servo mount has 4 holes to allow locking 4 axles and managing their respective cable.
For the other side of the servo mount I utilized a stock tree piece from a Tamiya truck. That part could be easily drafted and 3D printed as well, but I didn't do it for this project.
If you go with a 30% infile that is criss-cross and do a 2-3 layer top it will sort of look textured like a type of anti-slip surface, which is kind of cool. There is a photo of this effect above.