Quoted from xTheBlackKnightx:If a tool requires a grounded plug, there is a purpose. Cutting off grounding plugs for any reason exposes the user to electric shock, and make the person a hack. If an old EM has no built in game grounding, you add basic grounding for safety reasons of the player and maintenance protection of the technician. If a person is asking to fully modify an older game for convenience of using modern polarized electric tools with or without a grounding pin, this is not advised. The reason is straightforward, the game never supported this function, so do not do it, use an external connection for necessary tool power.
I actually have seen people do some less than intuitive things off both the power and neutral leads.
As an added note, I honestly don't like messing with old service outlets in general. May have corrosion internally (though don't have examples of this), but mostly I just don't like taxing vintage wiring with even a 2 prong soldering pencil (though I rarely use one).
I would not suggest removing/modifying the original service outlet in this type of machine; I see no point in stressing old wires around unnecessarily. Only exception I could think of would be if outlet/wiring was physically damaged or modified poorly in the first place.
I usually use an extension cord or occasionally use one of my trouble lights that has a 3 prong plug on the side of it (some only have 2 prong, but not hard to find a 3).