It is a battery combiner that connects your house and start batteries when a charging
source is present and isolates them when it is not. If you were reading -3.2A when your batteries were above 13.1V, then it was probably working correctly and that 3.2A was charge current
going to your starting battery. If it was reading -3.2A when your batteries were below 12.7V, then something is wrong with it.
The device itself should not be draining your batteries. Failed open, it will allow one set to go low without charging
. Failed closed, it will parallel your banks and you will draw from both. While this could be the culprit, I would be looking for something else also.
no longer sells them. They were rebranded by West Marine from Yandina. Yandina has a lifetime warranty on them and will repair/replace for free (yandina.com).
It is safe to run the engine without it, but only the battery bank the alternator
is connected to will be charged. If this is the start battery, then the house will never charge - and vice-versa.