Issue with turn signals in 70 Dart

With that much trouble with flashers, you surely have "other" troubles.

The trouble spots are fairly obvious

BULBS. Must be clean and tight, and of course "good."

SOCKETS. Must be clean and grounded

KICK PANEL CONNECTOR. This is in the left kick panel where the harness goes to the rear. Clean and tight

TS SWITCH CONNECTOR As above

TWO CONNECTIONS THROUGH THE BULKHEAD. To left and right front signal. As above

FLASHER and flasher connector

FUSE and fuse clips

WHAT exactly have you done for actual troubleshooting? "Trying stuff" is not. Very first thing you want to do is to access an easy point with a voltmeter. EG Turn on the key to "run" and stick your voltmeter into the power side of the flasher connector with the signal switch either left or right. You should have "solid" battery voltage there. That is if the battery is "fully charged" at 12.6, you should have at LEAST 12.0 right there at the flasher.

If not, next thing to check is both sides of the fuse. Might be rusted fuse clips, loose, or even a poor fuse.

Is the voltage coming INTO the fuse clip good? Be critical!!! WHAT IS the voltage at the fuse clip?

Get your diagram. "Jumper" around the flasher with a wire with "quick connect" terminals to fit the flasher socket

Look at the TS switch connector. You have flasher power going in. You have left rear, right rear, right front, left front all coming OUT on separate wires. Try the switch, check the voltage coming OUT to the various bulbs. Is it LESS than flasher power going IN? "Bad switch."