Hello all.
I work for a company that works on RVs.
We recently had a customer come to us with an 85 Fleetwood Jamboree that wouldn't start. It's built on a Chevy G30 with the engine swapped to a 396.
I figured this out and can get it running.
But an alternator issue has come up.
This thing has two batteries. One for the engine and one for "house." These banks are normally separated by an isolator solenoid. Which was one of the issues I have already fixed.
After I got the it running I realized the alternator wasn't working. I pulled it, got it tested and when it tested bad, I replaced it. After installing the new one, it immediately started charging at 18V. After a couple of normal checks I pulled it again and had the new one tested. Two different parts stores and it tested good at both. I re-installed it and still had the same issue.
I dove deeper into the wiring and realized the alternator was connected to the House bank (along with the starter) so it was probably reading 1 voltage while trying to get to another so it was increasing the output trying to get there but couldn't.
I rewired the start/charging system back to the way it should be. Alternator no has a direct connection to the engine battery. But now it isn't charging at all. While it was running, the engine battery voltage was sitting at 12.05 (+/- 0.01) and not going up.

It has a pretty nasty coolant leak so I can't run it for very long until I get that fixed.

I have replaced the connector on the alternator and that didn't help.
The main power wire for the ignition was connected with an alligator clamp. That has been replaced with a 40amp fuse and hardwired.

The grounds look "decent" but I plan to clean those up and check again.

Any advice is appreciated.

I replaced the Body ground with a fresh wire and a clean spot on the firewall.
No change.

Sounds like someone has been mucking around with the wiring and you are stuck sorting out their mess. So when the engine is running the alternator should be charging both batteries by energizing the extra isolation solenoid. When it is not running the extra solenoid should disconnect the "truck" circuit from the "house" circuit. That way if the owner runs down the "house" battery they won't be stranded with a run down "truck" battery and a non running vehicle. The alternator, starter, vehicle driving lights, and all the items for the "truck" chassis should be on that circuit. The alternator should be monitoring the voltage for the "truck" battery. Some alternators need a draw to charge. If the alternator does not sense a draw it wont charge at all. Most newer alternators are the one wire alternator type. In this instance you might need a 2 wire alternator to be able to use that second circuit to operate the extra isolation solenoid. I didn't see an output listed but it probably should be 40 to 60 amps at least.

I think you are on the right track but need to talk with the owner about getting his vehicle back to factory specs. It is going to take a little time and money to get the vehicle dependable again.

Please let the forum know what you find.

Art