I believe your flasher unit is fried. If you did not already check it, it is the silver cylinder under the dash just right of the steering wheel. It is a little smaller and shorter than a "C" size battery. It just plugs in. Pull on it and it should come out. A new one will cost about $8.

Check the ground  onnection to the headlite/ flasher.

The flasher is a current activated device, that is the current flowing thru the turn signal.lamps heats a bi metal strip in the flasher and causes it to bend and break the circuit. When the strip cools, it returns and the circuit is again completed and the lights etc etc.

If the ground isnt secure then the current from the headlight tends to "overload" the local ground to the turn signal light.

This in turn reduces the current thru the light and flasher so that there is not enough current to make the flasher work.

Check all the connections, esqpecially the vround, leading to the headlite, side marker and turn signals to make sure they are clean (that means shiny) and secure (tight fitting)

Also  check that the connections to the turn signal bulb base and socket are clean and tight so that the bulb makes good contact.

To check connections try wiggling the  connections and bulbs with the lights on to.determine if there is a loose connection.

You might also coat the contacts with battery corrosion spray to keep them clean.

Heres a link to a post here where you can find a link to a wiring diagram.

The pinto section starts about page 16 and has connector diagrams and grounding locations.

https://www.fordpinto.com/pinto-faq/for-those-with-1972-pintos-or-fords-link-to-the-72-ford-wiring-and-vacuum-book/