I have this same system. As Richard said I cleaned the bezel several times with a Qtip and alcohol retensioned the springs, and had to replace the switch. In addition I left the window open and water got into the control board underneath and had to be replaced. The parking light does not always come on and the system will not work. If I quickly press the parking brake it will engage. Having said all that if yours always works on shore power but not on battery power and your batteries read 12.4v or higher I would check your connection for corrosion or tightness. Just because you read 12.4v at the solenoid for the motor does not mean you are getting enough amps through to engage the solenoid. Try pressing the battery combiner switch if jacks work then, you know the problem lies with the chassis battery or the cables connections.