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My 86 #121 doesn’t charge the chassis batteries when the engine is running. For that matter the alternator doesn’t keep the lights etc operating either.  I have been driving with the generator running to keep all systems functioning. I removed the alternator and had it tested.  Fully functional with 130 amp output at 14 volts according to the shop. Where to go next? Chassis batteries charge from the inverter just fine.

[77newell]

On my 77 I had the voltage regulator die and corrosion inside terminals, not at the same time. Carefully applying 12v to the field wire terminal on the alternator and see if the alternator starts alternating as it should. Of course, if your alternator has a built in regulator forget everything I just said.

[Richard]

To add to the above, when the alternator is installed on the engine, does it produce voltage at the alternator terminals with the engine running? Lets cut the problem in half by figuring out if you have a wiring problem or an alternator problem

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An alternator shop bench tested the alternator. Putting out 14 volts and 130 amps. It has a built in alternator. I have owned #121 for about a year and have always had to run the generator.

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Built in regulator.

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Engine is down for radiator work.

[Richard]

Ok, got it. Built in regulator.

Look at this diagram. https://f01.justanswer.com/idrdb/c84b5ca...0-4900.pdf

With the internal regulator, you still have to have a power line that turns on when the ignition is ON. Since the alternator worked on the bench with correct wiring, and it has never worked on the coach, you probably have a coach wiring issue.

First thing to check, by looking at the diagram, is does the ignition wire have 12V when the key is ON. If so, move on to the main wiring. Starting with the main POS wire, trace it all the way to the batteries. It won’t go directly there, but trace it with an Ohm meter until you get to the batteries. Make a diagram.

Do the same thing with the NEG side too. Half of DC problems are on the ground side.

[Tf175]

What Richard said . If the alternator is producing those numbers on the test bench , it should function in actual service . Apart from the wiring , I suppose there could be a drive issue . Doubtful of that as the drive is very stout , like the entire engine . 
Check the wiring per Richard .
Chris

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        Thanks guys. The diagrams are very helpful. My alternator is wired as self excite according to the diagram. I need to spend some time tracing from there.  There is a confusing array of wiring behind the rear start panel that I need to trace out. Should have the engine running again in the next few days with a re-cored radiator.  That should help. But first I’ll trace out some of this wiring. What does a battery isolator look like? Is it a diode assembly essentially?

[Guy]

On a positive note, your wiring looks to be unmolested by rv techs or previous owners diy work

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The 12v wiring is pretty much untampered with. Except for those cut wires at the bottom of the rear starter panel. No idea what they are all about. Now the 110 wiring is another story. Lots of tape and random wires to nowhere.

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What is the rusty item at the bottom labeled “converter”?