Your brown wire at the regulator is connected to the key switch and shares the same terminal as a 12 gauge brown wire that feeds the fuse panel ACC stuff, wipers, heater motor, turn signals,. It is a 16 gauge brown wire to the firewall block and insde the FB it becomes a 10 ohm resistance wire to excite the regulator.
If you are getting juice through the key switch with the key off to the ACC terminal then you should have power on those fuses with the key off as well. The drain would show up as long as the regulator was plugged in because the brown wire is hot even with the key off. so it is closing the contacts in the regulator causing the drain.
this is why pulling the fuses did not stop the drain.
My suspicion is that the key switch is feeding the ACC terminal with the key off and you will see voltage on the fuses that the 12 gauge brown wire feeds with the key off. The wipers heater fan turn signals etc. will work with the key off as well.
I had a member with this exact problem a few weeks ago and it turns out that he had a burned connector on the key switch from years of heating and it had cause a short between the red power wire and the ACC wire in the key switch plug. Yours is not that because the draw went away when you disconnected the Ign switch.
Check the switch for continuity between the battery terminal and the ACC terminal with the key off and if it shows 0 ohms then there's your problem.
Here's the key switch with the black arrows showing the two wires. the 24 gauge wire is the resistance wire to the firewall block which connects with the 16 gauge brown wire to the external regulator. It shares the same terminal (ACC) with the 12 gauge brown wire that runs to the fuse panel.
Here's the 12 gauge brown wire going to the fuse panel to feed the wipers turn signals heater fan etc. It has a black arrow on it also.
