When reading about cool projects and products, it’s common to see wiring plugs labelled “JST connector.” This looks fine until we start getting hands-on and begin hacking things together. Inevitably we find the JST connector from one part fails to fit in the JST connector of another. This is the moment we learn “JST” is not a connector specification. It is short for Japan Solderless Terminals Manufacturing Company, Ltd. A company whose history goes back to 1957 and their website (styled in 1999) lists hundreds of different types. We can simplify to “JST connector” when chit-chatting about projects. But when it comes to actual hardware specification, that’s not good enough. Which JST connector? The reality is: we live in a world full of ambiguous connector specifications. We also sometimes choose to ignore “No User Serviceable Parts Inside” and merrily explore guts of equipment to which we have no specifications at all. As hackers, we need some skill at deciphering mystery connectors. We’ll start here with a quick survey of the most popular types from JST. A simple two pin wire-to-wire connector is probably the RCY series. When a connector interface two or more wires to a circuit...