ANY Single pole ON-OFF switch will work and either wire can go to either terminal, you are just completing the circuit. I am more than happy to offer support for anyone needing it.
UGHHH there is nothing worse than someone selling something that they don't even understand how it works.
This is not true. You need a single pole double throw. Not a single pole single throw. What this means for people who don't know much about electronics:
ignoring whatever contacts there may be to provide light and and a ground a single pole single throw has only two contacts and by pushing the button it either breaks or completes the circuit. Where as a single pole double throw, has 3 contacts call them 1, 2 and 3. 1(2) output and 2(1,3) inputs or vice-versa. when you have the switch in its activated position, it completes the circuit 2 to 1 and breaks the circuit 2 to 3. when it is in the deactivated state it breaks the circuit 2 to 1 and completes the 2 to 3 circuit.
This is very important because the wire to the back of the head unit needs to see a 12V signal. That's what triggers it to turn on the camera. Basically the way the switch needs to be wired is the lead from the back of the radio would get connected to pin 2. The other lead needs to get connected to the normally closed contact(pin 3 from my example). And a 12V power source needs to be connected to the normally open contact(pin 1) in my example.
If you mix up the two leads you will have created a switch that turns on your reverse lights when ever you want them.
Also a better way to control whether the reverse camera is to install a diode inline and a single wire lead coming off as a splice on the headunit side of the diode. That single lead could then truly be hooked up to to
ANY normally open single pole single throw(SPST), or single pole double throw(SPDT) with the other lead being connected to a 12V source. The diode would stop the 12V signal from the switch from traveling back through the car's circuitry and turning on your reverse lights.
Lastly I will touch on cost. (All pricing is from mouser, but digikey sells it too) and this is using the exact connectors that will interface with the oem harness which uses 3 of the 5 pins.
Male pin connector $0.10 each (need 3)
Female pin connector $0.10 each (need 3)
5 pin female receptacle $0.19 each(need 1)
5 pin male rececptacle $0.36 each(need 1)
1000 feet of wire $411.71(lets be generous and assume 10 feet of wire is used per "dongle")
wire loom (to make it look nice) $140.84 per 100 feet (assume 8 ft per assembly)
head shrink to go along with wire loom $1.26 per 36in lengths(probably need 6in per assembly)
Then you need a crimping and cutting tool. those you can get a basic one for around 60$ or you can get a really nice one for about 125$ but you only need to buy these once.
If he makes just 1 dongle it costs him a lot! (even if he only gets 100 feet of wire for 60$) but if he were to instead make 100 dongles at one time. Which is probably about average for production materials. He doesn't have to assemble them all at once. Total cost of materials is $2081.53(20.81 per harness) and assuming he wanted to get the nice crimps that makes the cost of materials per harness $20.81 the most expensive thing in this is the wire loom. If you instead used 3 zip ties per foot you could eliminate the wire loom and heat shrink and get the cost down to $759.11 or $7.59.
