HELP: Headlight switch triggering STARTER!!!

Also maybe an optical illusion but the 'alternator' wire from the ammeter doesn't look like its as big as the battery (red) one.
Definately want that to be 12 or even 10 ga (SAE) or 12 AWG. You said you were crimping and soldering so the connections are probably good.

Chrysler did use locking in-line 'bullet connector' when they ran those wires out through a grommet.
Example in the 4th picture down here
How rare is electric rear defrost?