[Flick]

So today i had the coach home and was going to plug it into house current to see if the charger would in fact charge the batteries as others have said it would. I used the pigtail from 50 to 30 and then another pigtail that went on the 30 that has an end that can be plugged into a house receptacle. I turned off the the house and chassis batteries and plugged it in. A very loud humming sound came from this box on the wall in the electrical bay. I quickly unplugged it because it did not sound correct. The pic below is the box. It has a toggle switch on the side that has an on position either up or down with middle being off. It made the sound in both on positions. Anyone know what this box is and have any ideas or suggestions?

   

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This is the front of that box with the lid closed.