74 dart can’t get a spark

I would start by finding out if the problem is in the immediate ignition system---that is the box, the distributor pickup and the related local wiring---or in the harness feeding the system

To do this, jumper 12V from battery to coil + See if you have a spark. You can jumper across the exposed terminals of the starter relay to crank, and check of course with the coil wire. BEST is to REMOVE the coil wire and use a SOLID piece of wire rather than resistor/ radio wire. You can even use "low voltage" wire if you "hang" it in the open away from metal.

With key "in run" measure do you have voltage at coil +? Should be NOT full battery, but "down" say 6-10V or so. If it is full battery it means the box and coil are not drawing current

Check box is grounded MUST!!
Wiggle distributor connector in/ out several times, they get corroded.
Connect distributor connector to your multimeter on AC volts and crank. Distributor should generate about 1V AC. Inspect inside of cap and around reluctor/ pickup for rust, debri, damage, and shaft wear/ wobble/ looseness

With key "in run" and coil wire near ground, disconnect distributor pickup connector. Take the harness end of the connector and tap the exposed terminal on ground. Each time you do so, should get one single "snap" spark from coil wire