Do you know that you have 12 volts from your battery source. Do have a voltmeter/ multimeter to measure the voltage? If not I woulD consider getting one, even a cheap one. I think it would be a good investment if you do any wiring. Also I know you said you "have two 6 volt batteries with cross-over connect for 12 volt use”, but do you know if the batteries are connected series or parallel? Series will increase your voltage giving you a 12 volt source, but connecting them in parallel, like when you do with jumper cables when you jump your car, doesn’t increase voltage, but instead increases your amp hour rating.
