Wires for the TRS jack
TRS audio jacks normally need three wired connections but we only need two for this project. Prep the wires by stripping a bit of insulation from the tips of each wire and apply a bit of solder to the strands to tin them.
We'll need to tie the two smaller legs of the TRS jack together. So I used a piece of header pins to do so. Each leg has a small hole in it, so I slipped on a single header pin to the holes, essentially bridging the two.
Then, I apply some solder to fuse the header pin to the two legs. Be careful not to melt the plastic housing from the button or the header pin. You'll want to work quickly or the plastic will melt – Avoid holding the tip of the iron too long when soldering.
Now we can attach the two wires to the larger leg and one of the smaller ones. Polarity doesn't matter as long as one wire is attached to one of the smaller legs, and the other to the larger leg.
You'll want to remove the plastic bit from the header pin and double check to ensure the solder joints are fully fused and making a solid electrical connections.