Welcome to FTE
Throwing money at the issue is only making you poorer, you need to have the problem properly diagnosed.
If you are in the SoCal area, call Bill at Bill's Auto Repair in Orange (714-639-3410). He is the BEST darn mechanic around on older Fords. He does most of the work for the SoCal Galaxie club members, and has done work for me. I highly recommend him.
There are other factors to consider. One is the ballast resistor (wire) mentioned above, others could be a bad ignition switch or point plate..and etc.
The ballast resistor is actually a wire on these models. Ignition switch to coil.
There's two different ones listed for 1973 Ranchero's.
It's prolly the first one, but who knows after 34 years what's been swapped around?
D1AZ-12250-A .. Ignition Coil Ballast Resistor Assy (Motorcraft DY-84-A) #16 gauge wire / color code red with green stripes / 1.30 to 1.40 ohms / 60" long.
D7AZ-12250-A .. Ignition Coil Ballast Resistor Assy (Motorcraft DY-213) #16 gauge wire / color coded red / 49" long.
