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The alternator on my coach (#121, 1986 40') has never worked. We have been restoring the parked coach so it hasn't been an issue. I removed the alternator and took it to an alternator shop. They bench tested it and it performed well so I Re-installed it the same I found it. You guessed it - it still doesn't work. Leads me to believe it isn't wired correctly. I have attached a picture to illustrate how it is connected. Any words of wisdom?    

[Tf175]

Have you tested the output voltage at the alternator ?

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Have you tested the output voltage at the alternator ?

2.1 volts

[Tf175]

Just looking at my old Leece Neville ,
Both of the studs are Positive. 
When it was in use there was a ground cable from one of the three mounting bolts to the engine .

[Tf175]

Correction,  the ground was from mounting bolt to rear of alternator as shown in photo . This alternator is not the original , likely different to yours .         

[Tf175]

Looking at your photo more closely , I believe both your studs are positive .
Disconnect the ground cable from left stud and try again .

[Richard]

Hmmmmm, I cannot find a picture of that particular Leece Neville alternator. Rather than take a chance on a miswire and frying the alternator, I would go back to the alternator shop that checked it out, and ask them for a simple schematic of how it is wired. I would also find out if the alternator requires a regulator or it’s an internally regulated model.

Then you can start to diagnose.

Some quick things you can do in the meantime. The large red cable on the right of the picture appears to go to ground. You can verify that with an ohm meter. Like Chris indicates, that post is USUALLY hot on other Leece Neville models. This may be a problem.

The small red wire should have 12V on it when the key is ON.

And you will have to trace the heavy red wire on the left into the coach to see how it eventually connects with your chassis batteries.

It is always a good practice to take the time to completely understand how YOUR coach is wired. Many times, previous owners have modified what was original. The potential for letting the smoke out of expensive electrical components is high by using wiring examples from another Newell WITHOUT confirming that the wiring example is consistent with your coach.

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All good advice. The wire in the lower right in the picture goes to the battery isolator. The heavy short lead goes to ground and the small red wire is live when the key is on. Alternator shop is a good thought. They seemed to think it was working fine based on the bench test. They even adjusted the voltage output slightly to 14V. Based on that i assume it has an internal voltage regulator. Any chance the drive on the engine is not turning? Seems unlikely.

[Tf175]

Looking at your picture both studs/posts are isolated from case ground by the white insulator . This indicates to me that these are positive . The one on left in the picture has the short red cable going to ground . I think this is wrong . 
You might ask the alternator shop how they wired it on the bench , as per Richard .
It is possible you have a drive issue , but I would think it would have been evident when you removed alternator. It drives off the blower shaft .
When I was going through Leece Neville I found information on the Prestolite site , spoke with a knowledgeable tech . 
I am looking for pictures of my original alternator,  it was likely the same as yours. 
Chris

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BTW , that is your external regulator with 14v and a part number on it .

[Tf175]

Also , have you tested voltage on the red cable that goes into the hinterland , with it disconnected from the alternator ?