I really enjoy using my MPCNC, but I've always been a bit uncomfortable about wire harness management. In particular, getting power and control to the gantry in a "clean" manner that also did not require any attachment to the gantry itself for best precision was the major problem.
Taking a cue from another user, I designed a carrier for the drag chain that clamps to the side of the XY piece along with a track using 3/4" aluminum angle and two servo mounts. I used the very good drag chain attachments from https://www.thingiverse.com/thing:1272581 to complete the routing of all the wires. I chose a clamp attachment method to avoid having to reprint and disassemble/reassemble the entire center piece of the CNC.
The center mount attaches with a clamp screw from either end of the side piece using a nut trap. The internal retention tab is beveled to avoid the axis bearings. The small piece spans to the larger mount part using a 6-32 screw, but it needs to be cut to length (approximately 1.7").
Servo mounts attach with 6-32 screws and nylox (or regular nuts) with a length of aluminum cut to size between them.
I ran Z-axis wires, spindle power (3 wires) and an extra wire for endstop across the mount. I used this drag chain, which is just about right for the number of wires: https://www.amazon.com/gp/product/B01M0WRHUN/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
The center mount also has a provision for a terminal block for spindle power connection, which seemed to work better than any connector option I'd considered.
Made so that the proper orientation does not require any supports.