Wires for Button
We'll need two pieces of wire to connect the button the ItsyBitsy board. These can be a bit short since the button will be mounted close to the ItsyBitsy. I made mine about 2cm (0.7") in length. I used 30AWG silicone covered wires for this because they're thinner and will need to be flexed quite a bit to install into the case.
Now we can attached the wires to the leads on the button. The wires will need to be soldered to the correct pins, so take note of which side they're connected. The polarity doesn't important so it won't matter which wires goes to ground or input on the ItsyBitsy board. There's four pins and a set of two have linked continuity. The two pins on the side of the body are normally open, while the further apart ones are linked. If you're not sure which leads to use, use a multimeter set to the continuity mode to see which leads are electrically linked.