Just curious if the alternator bracket is the same, I believe they are but can't be certain, the money pit is discharging when hot, just takes 5 minutes before it drops voltage, I'm sick of it, I tried to get a 3G put on it in the past, they went against my wishes and rebuilt the stupid 90 amp that came on it, its not the fire starter at least, but is externally regulated, was thrilled with my task of rewiring that, battery had leaked acid on the wiring and dissolved the entire regulator harness #2 reason I wanted to 3G it, glad I was forced to fix that! I have a digital dash gauge, reads 13.8 at start up, at the battery I get 14.1 or 14.2, about 5 minutes of idle the heat increases under the hood to an immediate drop 12.1 at the battery, 11.8 inside, need to have it load tested to insure if its the alternator or regulator, thank you ford for requiring battery removal to get the regulator out, I hate this pile of junk already, now if I find the issue is the alternator it is done, will 3G then start looking for a sucker with more money than brains to unload it on, satan seems to be responsible for this wreck, never hated ford more than now!
OK seriously, I've seen several videos of the swap, I did it on my 73 Econoline and learned true durability, the 3G is tough, I do not have the 2G on my 89, I think its the one used on Ambulances, not sure how it can die within 5000 miles, not shocked by anything anymore tho.
What I have, was built by an alternator shop, so its tweaked.
https://www.autozone.com/p/duralast-...queId=58879912

 

The regulator... Is it a Motorcraft one?
Aftermarket electronic regulators will drop out like that and usually fail completely shortly after
I am worried about your harness if there is acid damage, that's trouble
I would fix that first, in case it is causing the trouble you have
You remember those little plugs you would plug into the alternators voltage regulator to full field them, right?
I have one on my charging system tester machine
That's what I would plug into yours for testing,
* Or just jump the field to B+ at the regulator
NAPA 4-5033 & Thexton 342 are 2 of them that you just plug into the harness to full field the alternator

 

I am not sure on the regulator, can't see it, came from a parts store, I have the replacement off my 73, even have the older contact point one from my 73 if I can find it, reaching down in the engine bay today revealed the negative post on the alternator is bare, no wire, its grounded through the mount, so why have a post. I am checking the sketchy wiring, 4 gauge battery cable to starter, 6 gauge ground to block, which is skinned and jammed in one of those lead battery connections, very poorly I might add, thinking of running a cable to the bolt on the ground to the negative on the alternator, 4 gauge to insure that isn't it. If I could get at the regulator without having to remove the battery would be nice, I had to fix it 5 years ago, replace the end, I used but connectors instead of soldering it on. Its just so hot outside, and I have no shade, I want to get the guy who built it to take a look once I get the wires sorted out, he can test it. The gauge I added inside reads 11.8 when it drops, but at the battery, I have 12.2, shouldn't be different. There was slight corrosion on the positive, but was just on the outside of the band, which could interrupt the rear battery connection to the front battery, I cleaned that up, negative had none, but the frayed negative wire banded down looks like crap, I swear I remember having issues that had me questioning the grounds on this mess, I added an 8 gauge strap from battery to the radiator support, I need to find the block to frame to complete the loop, or just put a larger one in place of my 8 gauge.

This is about to be my solution, wire the alternator with 4 gauge wires, from post to battery both power and ground.


Yet at the battery post the volt meter reads 12.2

 

Positive on top, ground under it, stand on your head, don't drop the 8MM nut.
I checked the voltage regulator connection, when it drops voltage again, I'll swap to my other regulator, can reach the socket on the end, but battery must come out to remove the bolts from the regulator. Its charging, I turned my headlights on and dropped the lift out, once you power the wheelchair lift up to pump it back up in the van a heavy load is established, didn't even din the headlights, I've not finished creating the 4 gauge power cable, 150amp fuses came it today, looking ahead for a 6G conversion when this finally fails.