ground switch

Okay, I'm starting to service my own amps now and I have to ask something. A couple of my old Fenders have an adjustable ground switch on the back panel. What is it for and which position should I have it in?

I would ask an electrician.... I think it has something to do with the polarity of your ground wire (positive or negative). I think there may be a USA standard. I don't think it has anything to do with the sound of the amp.

I did a Google search, and there seems to be a lot of information on removing the ground switch and putting in a 3 prong chord.

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