One troublesome area on the connection path of our water heater is the push on connection on the post that is part of the control board. The post is not unlike the connection on a sprak plug. What happens over time with the expansion and contraction on the metals, the contact at the end of the wire that pushes onto the post expands just enough to rendure intermittant solid connection. With a 12 volt system this minute amount of voltage will cause the symtom you describe. Put a pair of pliers to the end of he wire connection and close the half circle openning so that you must push solidly to press it back onto the post connection. Hope this helps.