Alternator doesn't charge

[Happy Farming]

Hi all; I'm learning so direct me to the right forum, thread or where to look if I'm in the wrong place please. On a 1973 GMC 6500 with 366 engine, 10SI alternator with a factory ammeter in the dash. So story goes the alternator didn't charge, I replaced the rectifier, regulator and brushes, no charge still. But If I use a small jumper wire to connect the Generator node to the Battery node it'll charge. (This truck has two rows of connections on the firewall under the brake fluid reservoir.) ( The signal/ monitor wire is connected to the battery wire by the alternator but is now connected to the field on the alternator to allow for charging since the field wire doesn't show voltage with the key on or continuity to any other node on the firewall, alternator or battery connection.) (Don't try this at home unless you disconnect the battery after shutting the engine off since it'll drain the battery and the signal wire should be connected to the battery not the alternator field.) The battery wire from the alternator shows continuity to the Generator node on the firewall but not the battery node. I don't get 12v to the brown wire that was connected to the alternator field. Tracing the alternator wires (just brown and red since the yellow signal/monitor wire goes to the red wire that should eventually go to the battery.) they go on the intake toward the transmission then to a larger wire bundle. I'm guessing I lost connection to a ammeter/ shunt wire that from forum searching was supposed to be between alternator and starter (then battery) with an ammeter wire monitoring voltage drop across the shunt and wire from alternator to starter. But this GMC 6500 wiring sounds a little different than the pickups since I don't have two fuses on the firewall for the alternator especially since it's been worked on in the past. I'd like to keep it stock with the ammeter if possible unless like other ammeters I notice that don't register charge or discharge anymore. I might add a cigarette lighter so I can plug in a phone charger that reads voltage if no there's no better options but less wires = less problems as far this novice can tell. A side note: the points were replaced with an HEI years ago if that helps. I hope that all makes sense to y'all! Thank you for checking on my post and wish you safe travels!