What do I need to fix now

You have tools?


"What you need" for electrical troubleshooting:

A 12 v test lamp

A multimeter

Some "clip" leads. You used to be able to buy them at RadioSh$$t. I recently ordered some from Mouser Electronics

And...........a FACTORY shop manual. Thanks to some of the guys on here, you can download them free..........over at MyMopar.........The 73 is two sections, get them both

http://www.mymopar.com/index.php?pid=31

The factory diagrams were a bit convoluted in 73, so also get the aftermarket diagrams, which are simplified but not always complete

http://www.mymopar.com/downloads/1973/73ValiantA.jpg

http://www.mymopar.com/downloads/1973/73ValiantB.jpg

Clip your meter to the starter relay "push on" terminal which has a YELLOW wire going to it. Twist the key and watch the meter........see if you have battery voltage there.

If so, clip your meter to the remaining "push on" terminal. Don't disconnect anything, probe them from the back with the wiring still hooked up. This time, when twisting the key to start, you should have VERY LITTLE voltage, which correctly shoes that terminal is going to ground. That wire goes to the neutral safety switch (auto) or clutch switch (which you have to depress) with a stick shift car