Okay, everybody has told you one way or the other how to find your problem. Simply put do the following:
1. With the Battery switch in the off position take any and all wires off the battery switch common terminal.
2. Measure with a voltmeter from the battery common terminal to the ship's battery negative/ground buss.
- - If you are reading any voltage the Battery switch is leaking.
3. Install a new battery switch.
4. Repeat #1 & 2 with the new battery switch.
- - If you are reading "0" volts with the voltmeter in the 0-12VDC or 0-20VDC (depends upon the voltmeter scales) - fine. Reconnect all the wires to the common terminal.
** Part 2 - Assuming your boat has a DC ammeter on the panel . . .
5. Turn on the new battery switch which will connect a battery to the common terminal.
6. Turn off all the circuit breakers and disconnect any wires that are "hot wired" to the battery by opening its/their fuse(s). Leave all the wires that are connected to the common terminal of the battery switch alone.
- - Check each "load side" of each circuit breaker with the voltmeter measuring from the load side of the circuit breaker to the ship's DC ground buss. With the circuit breaker in the "off" position there should be no voltage showing on the meter. If a voltage is present you have a bad circuit breaker. Replace any bad circuit breakers.
7. With all c/b's off and fuses
removed, you should see zero draw indicated on the power panel ammeter. If not, there is a stray wire or something touching a feed wire in your circuit panel or your alternator diodes or battery splitter diode (if you have one) is leaking.
8. Find the stray wire and reposition it or replace it. If there are none then take your alternator into the shop and have it checked.