Diode in Series with E-Unit

My guess is someone tried to quiet it down. A full wave bridge would be better and adding a cap to the bridge is the best solution. You can tweak the mechanics to get them a bit quieter but someone more familiar with Post war will have to chime in. The bridge and cap trick has worked for me on a few extra loud E units.

Pete

   He noted he owned it since day one, so this is from the factory it seems?

  The diode might point at a coil meant for DC use, and I think that's one of the first NWs too isn't it? A post war factory diode? In series? Seems too soon? A capacitor in parallel maybe, but a diode?

No telling why for sure offhand.  But if it works jumped without excess coil heat, why not? The diode makes half wave which is half the ac power wave +pulses and so has a longer rest time, and so will likely be cooler than if you jump it.

I don't know why I didn't realize that, but you're absolutely correct, it was probably put there in some attempt to quiet things down. I have always been annoyed by the loud buzz most e-units make ... so I'm guessing I might have done that a bit more than 50 years ago when I was just beginning to experiment with electronics. I really don't remember doing it, though! So not even bothering with a full wave rectifier, I just put 1000uf across the terminals and Wow! Total silence, e-unit works like a charm. Aside from the heat issue which I don't think will be a problem, the only down side might be when the e-unit gets some more age and crud on it and gets a little sticky, I will no longer have the buzzing to help loosen up the mechanism on each change in direction  Thanks ya'll for shedding some light on a dim memory!