Guest battery isolators allow you to connect your engine alternator to both batteries or banks of batteries for independent battery charging. They'll also prevent a higher charged battery from discharging into another, lower charged battery, by keeping both batteries electrically isolated from one another.

These solid-state devices act as electronic valves that keep your charging system operating safely. When your engine(s) is running, both batteries are charged automatically. When used with a Guest non-field disconnect battery switch, you have complete control over battery selection for power use, plus alternator protection provided by the isolator. Models are available for systems with 10-120 amp alternators for 6, 12, 24 and 32-volt negative ground systems.

Selecting the Right Isolator for Your System
The first step in selecting the correct isolator is determining whether your regulator has isolation diodes. With batteries connected, ignition (key) "off" and battery switch (if you have one) "on", measure the voltage between the reg/aux/61 terminal and the engine block with a meter set on 20 volt scale. If the voltage reading is anything other than zero (0), there are no isolation diodes. If this is the case, be sure to order the required kit, #U-3059. The chart below lists the appropriate isolator for specific applications and alternator outputs. For outboard alternators other than OMC, order Model #2401A.