I have made a few Fritzing parts to my own use.
When opening the Kilomux Shield.fzpz file in my computer Fritzing makes one breadboard file, one schematic file and one pcb file to respective directory:
File names are something like: YTX_Kilomux_aaad1723b5b8dfafaa8ef4434638f890_12_breadboard.svg, YTX_Kilomux_aaad1723b5b8dfafaa8ef4434638f890_12_schematic.svg, YTX_Kilomux_aaad1723b5b8dfafaa8ef4434638f890_12_pcb.svg.
I opened and studied those files with Inkscape.
The part file Kilomux Shield.fzpz is not build from correctly made svg-files. Inside a part file there are a breadboard-svg file, a schematic-svg file and a pcb-svg file connected by Fritzings new part editor.
All tree svg: Breadboard-svg, schematic-svg and pcb-svg better have the same connectors that are named equally. For example: connector1pin, connector1terminal, connector2pin, connector2terminal, etc. The (connectorpin) names are free to choose but better be the same in every svg file. Connectorterminal names are usually needed in breadboard and schematic files. Using the same name if the safest way to name connectors.
There must be the same count of working connectors on every svg file.
At the moment Kilomux Shield.fzpz contains svg-files witch are defective in some respect.
Kilomux Shield Breadbord-svg contains 60 connectors in svg code. Non of those connectors refers to 5*2 male headers, which I think are the connectors supposed to use. They refer to the legs of 74HC595 and CD4067 DIP-packages. A breadboard likes to use female or male headers - not legs of a micro chip.
Kilomux Shield schematic-svg has 80 named connectors (not 60). The names are not the same as used in Breadboard-svg file. ISP-connector going to Arduino are not named at all. No big deal, but confusing.
Kilomux Shield pcb-svg has 60 named connectors from connector0pin to connector59pin. Not many has the same names as in Breadboard-svg file.
Fritsings new parts editor uses connectornames to connect the same connector in all three svg file. If they are not the same the part does not work.
There are a lot of user made parts. Opening one of them and studying the svg files in C:\Users\username\AppData\Roaming\Fritzing\parts\svg\user\ with new part editor and Inkscape learn you to make workable svg files to our parts.