house batterys not charging with engine running

Fairly common problem is that the solonoid that connects the coach and engine batteries when the engine is running, will both charge then when the ignition is off, seperates the coach battery from the engine battery so the coach will not discharge the engine battery. The manual switch brings them together to start if for some reason the engine battery is dead. I have had to change that battery isolaton solenoid on every camper I had (4 over the last 20 years or so) the only one that did not fail whas an old camper that used a solid state isolator instead of a solenoid.
I suggest you replace the solonid with one rated for continous duty availabale commonly at NAPA auto parts stores. Do not replace with the same trombetta solonid it probably has. It will not last.