Reverse polarity

tstone

so I took my 2000 fiesta vee 242 out today.  When I came back to the dock and hooked up.  My reverse polarity light came on when I turned my batt charger outlet switch on.   Leaving that off with just the main switched on all is good.   Just goes red after switching batt charger / outlet on.    Any help would be great.  Plz email me at thomstone99@yahoo.com.  Thank you

JC290

could be a ground issue on charger 

Black_Diamond

Or the charger itself.  Unplug the charger and turn on the switch, if it OK you know the problem.