1972 Dart Swinger won't start

You have to learn to troubleshoot instead of "throwing parts" at the problem. I am not making fun, I'm saying that is the way it is.

Start by (if you don't have one)

Wander over to MyMopar and download a factory service manual.........for free. Some of them there are due to the efforts of some guys on here

MyMopar - Mopar Forums & Information - Service Manuals

Also at that site is other articles and literature. Sometimes easier to follow but not always as detailed are the aftermarket wiring diagrams. Usually I prefer the diagrams in the shop manuals. These aftermarket ones are always two pages you can print them out

MyMopar - Mopar Forums & Information - Mopar Wiring Diagrams

There's lots more info archived over there

MyMopar - Mopar Forums & Information - MyMopar Tools/Reference

Next, it is important to understand how Mopar starting / ignition works, the difference between using the key to crank vs jumpering the starter relay, and to attempt to determine if the problem is fuel/ carburetion, general engine condition, tuneup, or electrical problems causing poor spark