Tiny,
Time to get the fingernails out!!! I just looked at a wiring diagram for a '38 Chevrolet passenger car and the light switch (stock) is pretty bizarre. The switch looks like it powers each front light individually. I don't know how the YNZ harness is wired, but the bottom line is, in a properly wired circuit, anything on the load side of a fuse will cease to function when the fuse is removed from the circuit (blown).
The dramatic discharge on the amp meter is telling you that current is flowing backwards to a ground. Your charging system might have a tough time overcoming this drain.
If you wanted to find the problem the hard way, you could recreate the scenario and wait for the smoke and flames...the problem would show itself!
Stuart
