Hi papacokes,
Welcome to the Heartland Owners Forum.
There are a couple of possibilities. The 120V AC goes to a junction box on the front inside corner of the water heater. If the wire nuts came off, that could be a location that's shorting to ground. If your water heater is just to the rear of the pass through basement storage, you can get to it by taking down the rear wall of the basement storage.
Another possibility is a short in the heating element. This can happen if the water heater electric is turned on when there's no water in the tank, or if you have a Suburban unit with a worn out anode rod. Anode rods should be changed when they show significant wear, usually at least annually.