73 Plymouth duster ignition

OK we need to determine what's going on. Try cranking it and listen close....and clicks buzzes, etc? Try again with headlights on. What do they do when trying to crank? Stay bright? Somewhat dim? Really dim? Go clear out?

What happens when you jumper the relay terminals?

You have a multimeter? You need one to work on these. And a 12V test lamp and some alligator clip leads.

Also do you have a shop (factory) service manual? You can download them free from MyMopar. Several of them posted there came from the guys on here