Wilfred, (Elizabethtown, KY)
To test the existing dual battery isolator, connect an ohmmeter from the center terminal to each of the battery terminals. The meter should indicate continuity only in one direction from the center (alternator) terminal to each battery terminal. Reverse the test leads to verify it’s only in one direction. There should be no continuity whatsoever between the two battery terminals. The isolator is faulty if you can read continuity in both directions between any two terminals or if you have continuity between the two outside terminals. When replacing a dual battery isolator, be sure it is rated higher than the total output of the alternator.
Another method of battery separation is accomplished by the use of “smart” devices such as the Sure Power Industries Smart Solenoid. These devices incorporate a high capacity, electronically controlled solenoid switch within a well monitored charging system. The Sure Power Smart Solenoid comes in two varieties; one begins charging the auxiliary system only after the engine battery has reached a minimum 13.2-volts. The other couples the two systems together in parallel when either battery has reached this pivotal voltage. Until then, the battery systems are kept separate. This is a much better alternative than a standard solenoid, but I personally like to see each battery system completely isolated from each other all the time.