Correct, Delco "voltage regulators" have a cutout inside, this is what disconnects the battery from the generator when parked.
I've been going thru a similar process with my SA, which uses the same regulator as the Cub. My original one is intermittent and the points are pretty far gone, sometime in it's life it got hot enough to melt the plastic that holds the lower contact of the points and has eroded the contacts. When it works, the charging current is only 1 Amp. So I decided to buy a new one and ordered one from a prominent vintage tractor house and put it on, didn't work out of the box. I took the cover off to look inside and the workmanship is very bad. The cutout points don't meet right, the upper contact holder was bend at about 45 degree angle down so when the points tried to meet they were just touching by a hair instead of the full surface of both contacts; cold solder joints too. Made in China, $32.95 wasted. I don't think these regulators are being engineered, just copied from the old ones and looks like a lack of skill in factory adjusting them to work properly. I guess if you can afford to use them like fuses, you'll find one that works.
So I ordered one thru Autozone, VR646
that crossed to the original Delco number 1118308, costs about 2x the other one, don't know where it's made but at least from a name company. And Autozone says if it doesn't work, bring it back for a full refund, no questions asked.
I rebuilt my generator and it bench tests good also except for the second part of the motor test. On the running tractor if I ground the F terminal I get a charge of about 8 Amps. With discharge of 3 1/2 Amps for the coil, that means the generator is supplying 11 1/2 Amps, which I think is reasonable.
On the bench test, I posted the question about the second part of the field test and got this answer.
I'm going to repeat the motor test on the tractor using the battery, it might be the battery charger I used can't supply enough current for the second part of the test.
I did a motor test on my generator using the battery and it spins when "F" is grounded and battery connected to "A". When I lift the ground off the "F" it continues to spin, not faster, but slower.
I installed the regulator from Autozone and it the system is charging. Good news, the regulator is stamped "Made in USA".
To test the system, I used a tester made by Allen Co. probably 50s or 60s vintage that I found a tractor show last weekend in Fredericksburg. I had to replace a few wires that had become brittle but it works great, especially made for testing generator/regulator systems. It has 4 leads, two for connecting in series with the batt lead to measure current and two to measure the regulator voltage. And the regulator test scale has a a green zone to tell you immediately if the regulation is in spec.
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