In its most commonly used wiring configuration, the common wire feeds the starter for the boat's engine. The common terminal is the one that gets connected to the other terminals. Terminal 1, terminal 2 and a common terminal. The back of this switch has 3 connections. When needed, the power can be cut to the amplifiers and locked out so that the driver cannot damage the speakers. The locking version of this switch and the previous switch are good choices for people who have expensive, powerful amplifiers and speakers in vehicles which others are allowed to drive. It's also available with a key to allow you to lock it. There are also options to break the connections to the field windings to the alternators but this one doesn't have that option. The one below can switch between two individual batteries, both batteries at once or can break the connection to the batteries completely. This type of switch comes in several configurations. This is a term used to many of the switches of this type, no matter the manufacturer. Most of those who use an isolator for marine applications have heard the Term Perko Switch. In this particular model, the 'key' is removable. As long as you don't mind having to manually flip the switch and can remember to do so, this is a good, simple solution. In one position, the batteries are connected. To use a battery disconnect switch like the one below to protect the starting battery from being discharged, you would simply connect it in series with the wire that connects the front and back batteries. The most basic isolator is simply a heavy duty switch (generally rated for at least 100 amps of current) that is used to make/break the connection between the batteries.

This type of isolator is slightly more complex to install than the most basic types of isolators. Most people opt for isolators that require no action on their part to keep the starting battery from being discharged. A battery isolator will let you completely discharge one battery without discharging the starting battery. This often leads to dead batteries and a vehicle that won't start. Many people listen to their stereo or use accessories (lights, radio, TV, computers, for those with RVs) without the engine running.

Stinger diode isolator