Measure them first. If the house Batteries, a set of four are 6 VDC, and they probably are see the attached diagram. If the chassis batteries are 12 VDC, and they probably are, then + to +...- to -.
The ground side to the coach is usually Black wires and bolted directly to the frame close to the Batteries. The Plus side is usually Red and snakes to components either in the engine or the Inverter if you have one. You can measure the resistance to ground, chassis, to find the Minus Side. Resistance on the plus side will be low and may make it hard to tell which is which depending on the quality of your meter. If you don't have a meter now is a good time to get one.