1974 Dart Sport Project

Get yourself a wiring diagram, or better yet a complete factory service manual. The 74s had a seat belt interlock that was a common problem when losing spark for no apparent reason. There will be a 3 wire plug on the drivers side inner fender close to the cowl. I believe you need to jumper the 2 yellow wires (sorry I don't have my 74 manual with me today) on the red plug to bypass it. The rest can remain unplugged. I hope this helps. This is not my photo. I just got it from Google images.
Cley
SEAT BELT INTERLOCK.jpg