posted 04-30-2015 04:54 PM ET (US)
I am not familiar with the internal construction of the BEP battery switch, but, since it is a rotary switch, I would expect that its contacts would make a wiping action when making or breaking. A wiping action ought to help keep the contacts free of corrosion, and, as I have often remarked, in a 12-Volt system the flow of current can be stopped by just a very thin layer of any type of non-conductive material.I suggest you approach the diagnosis and repair with this procedure:
--connect the negative lead of a reliable digital voltmeter to the battery negative circuit in a way that it is going to be a reliable connection, that is, you don't have to hold it in place with your hand;
--on the positive lead of to the DVM use a probe with a sharp point;
--measure the voltage at a number of locations, in each case using the sharp point probe and pushing it into the conductor firmly so it penetrates through any insulating layer; the locations are:
--the battery positive terminal;
--the battery switch common terminal; and
--the battery switch output terminal.
The goal of these measurements is to determine if the battery switch is getting power from the battery. When you check a connection point, check both on the ring terminal and on the post. You might find that, although the connection looks mechanically good, there can be an electrical stoppage in current flow between the ring terminal and the post.
If something looks odd, also check the connection between the conductor and the ring terminal by pushing the tip of the voltmeter probe onto the actual copper of the wire. Sometimes a crimp terminal can look good but not make electrical connection due to internal corrosion you cannot see.