By default JR connectors are intended only for use with r/c servos and 5V r/c power supply, but many of us are using them also for connecting other things such as video cameras, higher voltage or different types of interface. So there is a need to ensure that each receptacle goes into its matching plug, otherwise damage may happen to the equipment.
A similar problem is well known by airplane builders where a cable harness full with servo cables may come out of a wing and needs to be connected in the correct order within the fuselage.
One possibility to solve this problem is painting both receptacles and matching plugs with an individual color, but this still does not prevent from erroneous connections.
So I designed additional coder parts to be glued to both plugs and receptacles with using CA glue.
I have created 4 different codings, which is usually sufficient. In case you'll need more than 4, this is also possible, as JR connectors have an internal coding that ensures they will match only in one direction. So if you attach the coders to the opposite side of plugs and connectors, you will get 4 more codings for a total of 8.
I have also added the source from FreeCAD. The spreadsheet contains the code number (0-3), so the matching coder pairs will be generated automatically.
These parts are very small and near the limits of usual FDM printers, so you will need to add a little extra work with a needle file to get them perfect. I got the best results with arrangement as shown in the foto, although it would be possible to print both parts without support.