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I'm installing (hardwiring) a three pronged push switch to my stun-gun as a safety precaution. The components will all be incased in PVC pipe. To what do I connect the ground prong to? Thank you for your answer in advance.

Chris

In an isolated circuit, such as a cell phone (unconnected for a recharge), the "ground" is floating (unless you are speaking of the e-m radio ground). It is when you connect the circuit that the "overall ground" (probably earth, if you connect it to the electrical home distribution) becomes of importance.

In the case of a hand-held device, be sure that you don't allow the end user to touch (one hand or with two hands) to different part of the circuit which are with a difference in voltage (voltage is ALWAYS a difference of electrical tension). That includes the situation where the device is in charge, so it is nice to have the external casing at the same voltage as the domestic distribution system (the ground pin of the adapter).

One more situation where you could take into account, it is when someone opens the device (for possible repairs, as example). A capacitor may hold a lethal charge. A possible precaution is to add a circuit which will discharge such capacitors as soon as it sees light (opening the casing of the device). But a casing inside the external casing (a double casing) could ALSO be used, with a CLEAR label on the internal one about the presence of the electrical danger.

It is nice to care about possible dangers, but there are a lot of points to consider when handling high voltage. Before selling it or even letting other trying your device for comments, you should call the local authorities or certifications (CSA, ULx, etc. ) which are used to safety concerns and typical deficiencies.