re: Boat Motor won't start - help

When the voltage drops to zero is that a meter on the panel or measured at the battery? If it's just the panel it could just be a bad ignition switch. Turn the key to the on position and jump the starter solenoid with a screw driver. If it turns over you probably have a bad connection somewhere between your ignition switch (could be bad) and starter. If it doesn't turn over start at the battery and work your way towards the starter looking for bad connections.