50DN Alternator/generator Failure

[gus]

My 4107 alt stopped charging just before starting on a 4000 mi trip. I was expecting the worst.

Long story - short.

Turned out to be a failed three-position rear START switch. The circuit completion for energizing the alt field goes through this switch?? I jumped around it on the engine electrical panel.

This switch was one lump of rust, amazing it worked as long as it did! If this switch gets bumped off accidentally the engine won't start!

It took two minutes to solve this problem and two days going cross-eyed looking at wiring diagrams and the maint manual to decide what was wrong.

[zubzub]

2 days, you're getting good at this Gus.  Some would have taken longer, never solved the problem,  installed an alt that didn't need the excite wire, and patted themselves on the back for having fixed it.

[gus]

Zub,

I may never get another bus. I finally got all the mysteries of the 4104 resolved and now I'm starting over! At least it is another GMC and has lots of things in common.

I'm not all that smart, I bought a new engine kill solenoid and found out I don't need it, there was no power getting to it!!

That rear engine start switch is trouble in the making. It still controls the starting circuit and I'll jump around that when I have more time. Why only one set of poles failed I'll never know?

[zubzub]

Ah yes the rear switches mine mostly worked as well even though they looked like this...

[Brassman]

Oh my! Zubzub, that switch looks fossilized.

[gus]

I didn't even look at the back of mine but I'm sure it is just as bad! Not only that, the panel box bottom was full of dirt. The 4107 rear elect panel is not in a nice clean spot like on a 4104 and the cover is missing!

Once it worked with the jumper I quit because we're trying to get on our way to the west coast.