Since the horn is not working, its more likely the feeds into the connector than the turn signal switch.
Another good resource are the Chrysler Master Tech booklets.
Turn signal operation is explained in 1965, #2.
Master Technician Service Conference - Chrysler's Training for Mechanics
1968 has one that explains wiring diagrams.
On yours the H3 line is power to the horn and D2 power to the turn signal.
Generally the horn feed should always be hot when the battery is connected. So check there for battery voltage.
And the turn signals (D1 & D2) only get power when the key is in Run or Accessory position.
Trace D1 back on the diagram and it should eventually lead to the accessory terminal on the key switch. Check that one for battery voltage with the key in ACC
