That diagram is for a truck with an ammeter, to show net current flow it has to make that tortuous path. There's no idiot light on that diagram.

 

Ok, I see that now. The item marked "CHG" on the dash is the ammeter, and I misinterpreted it as the GEN idiot light.

 

I have no idea why this didn't occur to me before, but the '56 F-250 has been sitting in the garage 10 feet away this entire time, and there's a working voltage regulator under the hood.

Swapped in the voltage regulator from the '56 into the '64 and....drum roll....it works. 14.5 volts across the battery posts, 15.5 volts on the armature wire, 14.5 volts on the "batt" tab.

Could have saved an hour of two of tests if I'd have thought of that earlier. Oh well...

 

So the truck you bought as a parts chaser for your project truck had to be rescued by a part that you chased from that project truck!

Is that irony?

 

Whatever works. Good troubleshooting. Remember rust and corrosion (or paint) are the enemy in old (and new) trucks, this interferes with proper charging. Notice there is even a dedicated ground reference wire directly from generator to the voltage regulator, even though they are grounded to the fender apron. When the regulator loses its ground reference, then voltage can spool up to golly knows what.

The generator itself grounds through a pad or boss on the engine block, through the connecting bolts and bracket hardware. It pays to grind down to bright shiny metal. The rebuild I bought was nicely done but again had a thick coat of black enamel sprayed everywhere. I don't think it would have worked. Also ran a thread chaser tap through the boltholes and coat everything with NO-OX to keep salt spray and road grime off. Tighten securely. One thing that never made sense to me was why they moved the generator from up top of the engine to way down low, and exposed to all the rain and salt spray.

After replacing and cleaning up pretty much everything I checked for both 30 ampere output on my Sun and then took the truck on a little test run with an Innova voltmeter installed at the cigar lighter receptacle at cruise speeds from 30 to 65 mph, had never monitored charge voltage while underway before. (Yeah yeah, I know, "I wanna party with YOU".)

Was surprised to see hardly any sag when I flipped on the headlights and the heater blower on HI. It was running close to 15 volts which seems pretty hot to me but, according to the chart in the Shop manual this is exactly correct for the temperatures involved. Generator regulators have a higher setpoint than alternator regulators for some reason.

 

No kidding! I think my '56 found it funny too. Young punk '64...

The 1956 voltage regulator base is different from 1964. It's smaller and only 1 hole lined up perfectly. One other hole only lined up 1/2 way, so I just threw a smaller screw in there to hold it down.

Great point on the grounds. I'm going to run extra grounds all over the place when I wire the '56...