Ignition wires get warm
Normally you should NOT leave the ignition switch on for a length of time
Breaker points ignition---hard on points and coil both
Mopar electronic --will warm up the coil and the box
Other brands............MSD probably no foul. GM HEI module does not draw current with key on. Others I don't know
The above has nothing to do with your problem, it's simply a warning
I'm with Red..........
First pull the field wires off the alternator, and unplug the regulator. If this does not slow down the problem,
Disconnect the ignition, depending on "what you have." If points, unhook one end of the ballast. If Mopar ECU, unhook the connector at the box
Be careful. None of this stuff is fused, other than the main fuse link, which is damn poor protection. If it still seems to be heating with the above disconnected, IMMEDIATELY shut it off.
Also realize that "the key" feeds "other stuff." It is important to determine which specific wires are hot
The switched lead feeding to the fuse box switched buss may or may not be getting warm
while the ignition "run" line might be, and vice versa.