Proper polarity must be observed. The output side of the voltage regulator usually has three wires. One marked battery 1, another marked battery 2, and the remaining wire will be a ground. The battery 1 and battery 2 wires may be connected to either the terminals on the back of your battery switch marked 1 or 2 or directly to the positive terminals of two separate battery banks. The ground wire may be connected to the negative terminal of any battery or directly to the block of your engine.
Solar power is clean, quiet and unfortunately, rather expensive.
There are no cheap deals on solar panels and you will only get what you pay for. As with any electrical project, take your time, be certain of polarity and voltages and don't even think of attempting the project if you are not absolutely comfortable in doing so.