Verifying the Isolator if Functioning Properly

December 21, 2013 3:48 am


To determine if an isolator is functioning properly you will want to use a volt meter to check the voltage on both sides of the isolator while the engine is both running and not running.

The following are common steps on how to check a battery isolator  provided by the experts at

  1. Set your volt meter to DC voltage
  2. Touch the meters black probe to negative terminal of the battery or other common ground.
  3. Touch the meter’s red probe to the battery’s positive terminal.
  4. With the engine NOT running the reading should be somewhere in the 12.7 volt range.
  5. Now start your engine.  Immediately apply the meter to the (primary) starting battery.  You should see the voltage rising from 12.3 or so upward.  When the voltage meter reaches 13.2 volts the isolator will activate (indicator light illuminates)
  6. Once the indicator light is illuminated you should have the same voltage reading (13.2 or greater) on both batteries verifying that the battery isolator has closed.
  7. Now turn the engine off.  Apply the voltmeter to the primary battery.  The voltage will slowly drop to a level or resting voltage of around 12.7.  When the voltage drops to 12.8 or lower the isolator will disconnect and the indicator light will go off.
  8. Repeat the process but immediately when the vehicle is started apply the meter to the secondary battery.  Before the isolator’s indicator light illuminates the voltage will read 12.7 or so.  When the isolator illuminates the voltage will raise to above 13.2 thus verifying that the system is fully functional. (Call us now if you are still confused on how to check your dual battery isolator?)


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