Sounds like where you are plugged into the Shore Power is missing its GROUND wire protection. All three conductor must be connected...
Are you plugged into an extension cord that is plugged into a garge 120VAC Receptacle?
It could be the 120VAc Receptacle is missing the green wire GROUND connections... Get one of these circuit testers from LOWES and plug into your 120VAC source receptacle. It will tell you if all is connected properly...
Must be a full moon tonight...
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Do not plug in your trailer any longer until you can determine the source is ok. This may not hurt a grown-up but might be fatal for small animals or a small child etc... Very dangerous situation for you...
If you are plugged into your garage 120VAC receptacle do not use one of those small round adapters... Pick up a RV30A to 15A LONG dogbone type adapters from WALMART back in the RV section... Will look like this
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Also if you are using an 25-foot extension cord this must be at least a 12-gauge type... 10 gauge is best to use. DO NOT use one of those RED-ORANGE extension cords from WALMART. They will over heat and burn up your adapter or main shore power plug etc...
Roy Ken