I have an Oday 28, and have been putting her in shape over the last year. Redid most of the wiring when I repowered her. However, I didn't have to do much with the shore power panel or any 110 circuits. I have the main switch, the water heater, the outlets, and I understand all of these. However, there is one toggle named "Spare" and has a light associated with it. What is the spare for?