More Electrical Help ...

Well. It's an interesting puzzle.

Here's how the key switch should work.
In Start.
Power available at Ignition 2 (brown) and should show up at the ballast resistor connector J3 - J2A. Current should flow to coil whenever the points are closed.
Power available at S2 (yellow) which should close the starter relay. (internally connecting A1 & S5)

In Run, the switch connects power to:
Ignition 1, J2 which should show system voltage at the ballast resistor connection with R5, (blue - blue connector)
and on the same terminal is G5 going to the oil pressure light.
Accessory, Q2 which supplies power to everything else that runs with the key on.

One set of fuses gets power from a tap into Q2. They're only hot when the key is in Run.
Another set of fuses gets power from the main splice. So they are always hot if the battery is connected.
The instrument lamps have their own fuse - power comes from the headlight switch.
In the diagram, your fusebox looks different but concept seems to be the same as later years.

Returning to the clues:
The radio and heater fuse are on the Accessory side.
They should have nothing to do with the Brake light switch - which should always be hot.
So, somehow wires are touching or misconnected.

Back to the business of the ballast resistor getting very hot. That's also not right.
Key off. No current or voltage should be there.
In Start, it's possible the voltage regulator tries to let current through from the brown wire to the alternator field wire (green). But even so, it should not draw much current and so should not get hot.
if it gets hot in start, there could be a short to ground anywhere in the J2 or R3 wiring.

In Run, the only current flowing through the resistor should be going to the coil. It should get warm but not sizzling hot.
if it is getting excessively hot in run, there's probably is short in the J3 or J2A wiring (including the coil).