House battery only charging when switch is set to "both"

[stpinetree]

2015 RZ2. Boat is new to me. Has the promariner proisocharge, when the engine is running it only charges the crank battery if the battery switch is set to "on". If I set it to "both", both batteries will charge. It doesn't seem right to me to have to switch the red switch back and forth. Something wrong with the isolator, or maybe something is not hooked up properly? Any ideas?

[JCP]

Check fuse on the battery terminal.

[chpthril]

Those procharge units have been known to fail. This time of year, another possible cause is a rogue cable thats gotten left off will installing the batteries. If you have a basic volt/ohm meter, you can test the procharge.

[stpinetree]

Thanks. I'll pull the batteries out and check, more carefully. I do have a multi-meter, can you point me to how to test the proisocharge?