Turn off connector with a single switch
Now, of course I could install a small switch on every wire in the cable, but it seems silly to install 24 switches or whatever. Is there a way to make all the wires go one way or the other using just one switch?


Yes, but rather than involving active electronics, you can just use a 24-pole switch. Such large switches were once fairly common computer accessories, used to select one of multiple peripherals to be used with a port that could only use one at a time. They were known as “data switches”, and they had a common look despite being made for a wide variety of interface types:



I'm not certain that all such switches with 25-pin connectors would actually have 25 separate lines, but I think it's worth taking a look (and a continuity tester or a screwdriver) around the nearest surplus electronics shop, rather than necessarily building a similar device from scratch. You could either build an adapter from your connector to DB-25, or open it up and replace the connectors.