Need some help with diagnosing my car. Young guy learning

General help on diagonosing electrical:
Electricity flows from high potential to low potential whenever a circuit is complete. That is a path back to ground on the battery or alternator.
The car has two sources of power. When a circuit is complete, current will flow from whichever one has the higher potential.
Engine off, the battery is the only source of power.
Engine running, the alternator should be the source of power. If it's output voltage is higher than battery voltage, then alternator supplies power.
That's the basics.

Do a visual and physical check on the main circuit, on the branch that doesn't work consistantly.
Get or make a test lamp, and get a multimeter so you can measure voltage and resistance.
These tools will help find trouble spots when they are not visibly obvious.
Chrysler included an ammeter in their cars and trucks. It indicates current flowing to or from the battery. Pay attention to it and it can be a useful tool.
Keep in mind that 1975 main feeds may be a little more complicated than shown in the schematics shown here. But the concept is the same.
Understanding Charging Systems with Ammeter

Learning to read the factory electrical diagrams is a big help.
Highlight or redraw the circuit you are interested in. That makes it 10 times easier to understand.
Chrysler had series of booklets and films for the service techs. They are a good resource.
Probably the best assemblage is here: Master Technician Service Conference - Chrysler's Training for Mechanics
There's a website called "mymopar" that has some that the Imperial Club does not. They also have some Service Manuals available for download. If you don't have a CD or print copy, this is a good and perhaps your only option until you can get one. A lot of their stuff has been copied without credit or permission so quality of the scans varies.