Your SyMBplexer has a network splitter built into it, it is the small unpainted board that has three connectors on it and connects to the two round connectors on the back of the SyMBplexer, we used these round connectors for the network as they were very strong and easy for untrained people to use.

The SyMBfile cable connects to the flat connector and you can plug two Apple IIs in via the round network connectors. If you want to add more than two computers you need another splitter identical to the one in the SyMBplexer.

Your SyMBplexer has 4 lights, 

http://www.brutaldeluxe.fr/private/symbiotic/symbplexer/IMG_4783.JPG

on startup 

- the power light should come on
- the other lights should come on gradually as the system starts up, in reality the system starts in a fraction of a second but the marketing department wanted flashing lights so the firmware makes the lights flash for a while. The later units used square LEDs as they were more high tech - just a pain drilling the holes.
- if the SyMBfile is connected the SyMBfile access light should flash as it loads the boot code after the boot up.
- If you access the SyMBplexer via the network the the SyMBnet access light should flash.
- The processing light will flash from time to time - it means nothing apart from the SyMBplexer is still running.

If the lights do not flash on startup then you have a problem...

The SyMBplexer will receive network requests from the Apple II and direct them to the SyMBfile - it is a disk server with caching not a file server so it does not do file locking. It does have a flag system and a more advanced semaphore system used by database products such as Omnis, 4thDimension, eMail (the original Microsoft mail for the Mac, it was called something else then) etc. There should also be a software program on one of the floppies to download software to the SyMBplexer - the initial use of this was for the SyMBstore which could be plugged into the SyMBplexer and then operated remotely from a Mac or an Apple II by sending messages to the software running in the SyMBplexer.

To connect the Apple II via the network you can make a cable similar to the black cable running from the Fast Noxy in the SyMBplexer to the splitter board and connect this from the Fast Noxy in the Apple II to either one of the other two connectors on the splitter board - do not connect the +5V wire from the Apple II connection (it might be disconnected on the PCB), the other wires should be fine but keep them cable fairly short. The missing components on the splitter board is OK, they are for the power supply which is not needed when inside the SyMBplexer as it gets it’s power from the Noxy cable

Good luck!

David