The "Overload" light and alarm is to tell you that the devices connected to the UPS are drawing more current than the UPS can safely provide with battery backup. You should disconnect a few items, and the alarm and overload light will turn off. The "Building wiring fault" light on the back is to tell you that there's no proper ground wire inside the wall outlet that you're using. These two problems are not related to each other.
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The "Overload" light and alarm is to tell you that the devices connected to the UPS are drawing more current than the UPS can safely provide with battery backup. You should disconnect a few items, and the alarm and overload light will turn off. The "Building wiring fault" light on the back is to tell you that there's no proper ground wire inside the wall outlet that you're using. These two problems are not related to each other.