split wiring harness into two with mechanical switch

My project involves connecting to a pre-existing 8 wire harness from a machine (dupont sized holes, confirmed dupont wires fit nicely). I have successfully connected my arduino + peripherals to this 8 wire harness, and everything works as expected.

Originally, this harness connects to another harness which has a destination of a built-in console that would drive the machine. My goal is to "splice" my arduino setup at this harness-to-harness point and have my arduino be a secondary way to drive the machine.

My question: what is a good approach for splitting an 8 wire harness into two, such that I could switch between them mechanically? Ideally I would like to avoid more complexity for switching betwen them, and a mechanical swtich seems like it good be a good fit? e.g. if switch is position A, then all connections go to original destination, if switch in position B, all wires go to arduino.

I have tried searching for pre-existing parts or diagrams of this situation, but not having much luck.

Thanks for any suggestions; I would like to avoid disconnecting / connecting the harness each time I switch between original destination for the harness and my arduino as the destination.

8 pole switches are a speciality these days.

Would you be looking to hot-switch this bus?
What is the machine? What voltages are on the bus?

Thanks @MarkT for weighing.

The machine is an exercise bike and the console want kaput. Built a fun little console on the side to drive it, but ended up fixing the old "built-in" console as well. So would like the option of using either. All the wiring from the bike comes into a single 8 wire harness that connects to the built-in console via a male-to-female harness connection.

It's got 9 volts coming through one hot wire.

While it would be nice to hot switch, definitely not necessary. Could just unplug the bike and switch, then plug it back in. It's all just for fun and experimenting really.

I'm kind of new to electronics after dabbling my whole life, but I'd like to learn some sound principles. I guess I can see how mechanically switching that many wires is tricky, because depending on the mechanical approach, it could sweep across the poles switching them one-by-one and not all at once. Almost need like a up-down or out-in motion to switch cleanly, it feels like.

Any ideas or places to look appreciated.

There are 8PDT relays which don't come cheap. There is also a possible use of 4 each DPDT relays. Then there is always an 8PDT switch (mechanical).

You choose depending on the signals switched. Voltage & current for starters.


Its got 9V and GND presumably so likeley you dont need to switch all 8 wires.

Try it, the worst thing you can do is fry it. I would highly recommend you turn the power off when switching, I do not think those circuits were designed to be hot switched. You are measuring 9V, what is the reference point ground or some other signal?

Thanks all for the comments and suggestions.

Good to know about 8PDT switches (even that term "8PDT" I wasn't aware of, but that opens up a bunch of Googling). Is it just me, or do there appear to be far more 6PDT?

And that idea about 9v and GND.... that's a great idea. Feel like a single switch could toggle that. I'd worry about leakage? Feels like voltage from the arduino could travel up the other side of the Y-split? But perhaps I am thinking about that wrong.

The 9V was measured coming out of a single wire in the harness, and I traced it back to the 9V DC source coming from the wall + AC/DC converter box.

Just picked up a L298N DC Motor Driver that I think will help send > 5v to the motor, and then a regulated 5v to the arduino. The primary thing being controlled is what I've learned is a "dumb" servo in that it's got 5 wires coming out, and three are just to monitor the position. It's been a real hoot reverse understanding (even found the original patent of this device getting controlled).

While I have used 6PDT switches there are 8 pole versions. I doubt they are inexpensive but figured I would toss it out there. :slight_smile: I would suggest you carefully review things to know if all 8 lines need switched as was suggested. :slight_smile:


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