I cannot imagine that the brake light circuit is somehow related, unless some wiring has melted IN the harness(es) and cross shorted. Someone mentioned above--might be pedal movement---which is somewhat close to the ignition switch wiring---might be pulling on a wire connection, etc. Get under the dash, do "wiggle" test. Inspect the column connector for the ignition switch, and get a test lamp and meter and some jumper leads and actually do some testing
A couple of things:
This might not be related, but 74 has the obnoxious annoying Federally mandated "seat belt ignition interlock." Look on the left fender apron for a box about the size of a horn relay with a push button. This is the reset for that interlock system. The yellow start wire goes through that. Find the two "yellowish wires" and splice them permanently together
Also, partly because of the interlock, 74 has a unique wiring system. I created a 74-only electrical system from the factory 74 manual. If you don't have one you can download the electrical here:
Go down to post 64 and click the black icon in the box, "save as"
Free service manuals
Also go over to MyMopar and download the two page 3rd party diagrams. These are NOT as complete and detailed, but can be easier to follow
Get your meter/ light and go over both parts of the column ignition connector and see if you have power on the "start" wire. In the electrical section I posted, there is a section after the diagrams that pictures all the various connectors
View attachment 1715792404
The "start" wire is the top terminal yellow. This should be hot anytime you twist the key to "start."
Then go out to the bulkhead connector and the start relay, see if you have power on that yellow at the start relay, and if not, go to the bulkhead connector and see if you have it there
FUNCTIONAL PATH
The functional path which the starter relay takes is...........ignition switch--out on yellow---through the firewall connector---through the seat belt interlock---to one "push on" flag/ spade terminal on the start relay (coil)--through and out the remaining flag terminal--and either down the firewall to the automatic neutral safety switch, which is grounded in park/ neutral, or on a "stick" car, back into the interior through a grommet, and to the clutch pedal safety switch which grounds when pedal is depressed