This is not really an electronics project. It is a fiddly soldering/wiring /switching project, but someone used to assembling electronics should find it fairly straightforward.
I am a photographer. I need to use one to four cameras to trigger a large number of flash units
A camera flash trigger is created by shorting the pair of wires that leads to the flash unit
I need a box that allows me to 'short' multiple flash units, and to have some flexibility to separate or to join multiple groups of flash units
I have standardised all my wiring into mono 3.5mm jacks and cables so this unit will match that and will use 3.5mm mono female sockets
The diagram i have included shows my thinking - 4 inputs leading to 4 circuits of 4 outputs that can be joined as needed by using the 3 'circuit joining' switches that merge adjacent groups into one
The test buttons are important - they allow me to short single outputs without affecting the others, so rapid testing and fault finding can be done from the box
I am based in london