Here's how Mopar start/ ignition switches work:
You have (normally, some dissent) dark blue, "ignition run" or "ign1" which is hot with key in "run" and supplies the top end of the ballast, the regulator, the field for isolated field (70 and later) alternators, the electric choke if used, and maybe the carb idle solenoid if used.
For starting, there are TWO separate circuits. When you twist the key into "start"
Brown is hot, which BYPASSES the coil/ ballast resistor, and provides a hot spark for starting
Yellow goes to the starter relay, and on auto cars or cars with clutch safeties, a second "push on" terminal of the relay must be grounded through the neutral safety or clutch safety switch, to fire the relay, which then fires the starter through the "square" exposed terminal on the relay.
So you brown is either unhooked, or the bulkhead connector is "losing contact" or there's a bad connection between there and the ign switch (connector at the column) OR the ign switch itself is bad on that circuit
You can download a free service manual right here:
http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download
