I just purchased a 1997 cng e350. The rear tanks work fine but the front / side tank valve is closed. It has 12v to it and should be open but it's not. There is another switch / sensor on the valve that has 3 wires going to it 1 / ground...2 / has 3-6 volts...3 / nothing....can anyone tell me what this switch / sensor is and can it be the fault that my tank valve won't open. thanks