I have an old Fender SR and it has a plug with only two prongs. Ive noticed when I touch things like mics or other people guitars while having my guitar connected to the amp, I get shocked or they get shocked. I was wondering if there was an adapter or something I could purchase to stop this from happening. Or would the only way would be to rewire?

I also noticed I had a ground switch on the back that I could switch from + or - (i think). I always forget to use it but do you guys even think will be helpful or is the root of the problem something totally different from the ground?
I was playing on an old peavey keayboard amp that was shocking me through my guitar, the guy who owned it told me to flip that same switch that you are talking about to reverse the polarity, fliped the switch and everything was fine.