Generally speaking, if there is a loose connection ANYWHERE in the chain, either in the power or the ground, you can get intermittant operation. After you check for loose/corroded battery connections, you might look for bent pins in any of the connectors, loose grounds, etc. If you have a loose connection somewhere, the inrush current will sometimes pull the two contacts (pins/terminals/etc.) together and give you a good circuit. Other times they will not. Loose connections of many different kinds are a PITA in the electrical world! Finding them is the hard part, unless you happen to luckily stumble accross something obvious. Even if you do find something wrong, continue to check the entire starting system as best you can. A slightly loose connection will not look bad, so you will have to possibly jiggle the wires around while a friend tries to operate the start system. Find someone who is good with electrical schematics if you are not. These are the "Roadmaps" of your electrical system and a skilled individual will know exactly what they are looking for. Hopefully, the schematics are included in the manuals with the RFS's. Good luck!:)