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Am I doing something dangerous by not grounding my 5-way switch to the volume pot? I recently opened up my guitar and realized I haven't had it grounded for quite some time.

There's really no danger, per se. In a worst case situation, where you plug into an amp that has an extreme fault, and is applying voltage to the ground terminal of the guitar jack, that voltage will be applied to your bridge and strings, which will be a much greater risk than the switch.

I only have the 5-way switch grounded on one of my guitars, and even then, only because it was a convenient place to tie grounds together. (Tele)

So if I wanted to ground the switch, which lug on it should I solder to? I have both the hot leads from my two humbuckers on one side. The only lug on the other side of the switch in use is the common which is connected to the common on the other side which then goes to the volume pot.

Thanks

You don't want to ground any of the lugs. Those are quot;hotquot; terminals.
You would only ground the switch's frame. Some of the cheap-ish foreign made 5-way's have a ground lug right on the frame, but none of my American made 5-way's have that lug - so I haven't grounded them.

So, it becomes a matter of finding a place to connect a ground wire. Perhaps under a mounting screw. But there's really no need unless you're having some specific problem.