[kaptain]

Hello Gurus, 
I have a question regarding my Powerline model 33-53 battery isolator (please see pictures attached). 
When I check voltage across "A" to ground; "B" to ground; "C" to ground -- I get 12.4vdc. My question is on the voltage across "B" to ground... If the diodes in the isolator are operating correctly, shouldn't the voltage be 0 between "B" and ground?
Thanks for any insights.
Paul

Power line 33-53 the middle “B” is the INPUT terminal, which connects to your alternator’s output. The ‘A’ and “C” are the output which connect to your house and chassis batteries.

Now assuming you never disconnected any wires bolted onto the isolator when you made your measurements:

If your engine was running when you made the measurements, the “B” should has a voltage around 14 or 14.3V, and “A’ and “C” should read about 13.5V 

If your engine was not running when you made the measurements, then the “B” to ground should theoretically be 0 because alternative output was 0, but in reality, it can’t be 0 because diodes aren’t perfect, they all have small leaks, albeit small. Usually the large the rated capacity the more leak current. So your measurement readings can vary depending on the leakage and also depending on your voltmeter internal resistance, that making voltage reading here almost useless (unless you are ready to do some calculations with the entire leakage including the alternator circuitry and meters internal resistance etc), To get a more meaningful reading, add a 10 ohm or 12 ohm resistor across “B” and ground (make sure it is at least 10watt resistor just in case your isolator is bad), then measure the voltage between “B”, and ground, it should read 0 or nearly 0. Anything larger than near 0 then you have a bad isolator.

Make sense?