73 Dart No Headlights, Turn Signals, Brake Lights, or Parking Lights

What does the 'alternator' gage do since you change the hazzard or turn signal flasher unit?

That gage is an ammeter. It's shows whether the battery is discharging or charging.
When the engine is running, it should indicate either battery charging or be centered.
If it the battery is discharging while you are driving, then something is wrong with the alternator or its wiring.

What should I do/look for?
1. Check what other electric circuits are working or are dead.
2. Then with these clues look at the general circuit scheme to see what the dead ones have in common.
I'll post a generic scheme here. You'll may have to look at the shop manual diagrams to verify and fill in the details.

upload_2020-7-10_18-12-49.png

The basics of the wiring are this:
With the engine off, the only power source is the battery.
The dome light draws power though the 'always hot' portion of the fuse box.
The parking lights, brake lights and hazard also draw power through the 'always hot portion of the fuse box.
Check a '73 shop manual or owners manual for which ones share a fuse.
The headlight switch has two connections to the main splice.
Power for the headlights does not come through the fuse box. Instead there is an internal circuit breaker.
upload_2020-7-10_22-10-39.png

'73 Dodge FSM shows the hazzard and stop lights get power from the same circuit as the dome. Verify that if you can but testing all of those things will narrow down where the problem(s) are.

edit: And Tooljunkie is correct in that the turn signals only get power when the key is switch on. So they get power from the 'accessory' feed to the fuse box and are on different fuse (not shown in the sketch above).

If power is not getting to a light, then there is a break in the circuitry or possibly a short (two wires touching in a way that provides an easier path to ground).
If an item doesn't turn on but the ammeter moves to discharge, then suspect a short.

An break or corrosion can be on the ground connections too.