How do I plug in a 3D noise to principled shaders displacement? This noise node seems to render fine in the base color but doesn't work in the displacement.

vimeo.com/219038609#t=3032s

Just turn on the checkbox in Custom Input.
(yes, it's easy to forget it )

thanks for the video. I had limited success. It sort of works when I attach a fit node before I plug the noise to displacement. But not really. I tried to connect a texture and also aanoise and I felt like it didn't behave correctly. For example when I put the maximum displacement parameter to 0 it still looks like a rock. And the checker texture which looks fine when I use the texture field also didn't looked clean. Looked almost good with a fit node. (I used the rubber to model with just a simple principled shader)

Maximum displacement doesn't affect the amplitude of the displacement. When you use the disp/vdisp input, that's your input networks's responsibility. ‘Maximum Displacement’ is a hint to the shader how much additional displacement you have added so that the displacement bound is set accordingly. Displacement requires bounds to be predetermined by you otherwise the result may look unsatisfactory.

Thanks, I think I got the hang of it. Also I found out that it helps restarting the render when making changes and unexpected things start to happen.