1980 pickup new alternator starterand battery - was moving right along last night when I lost power to everything but the headlights. No crank or attempt to turn over. The only sign of battery life is the headlights

Looking around today nothing is apparently disconnected.

Interested in learning how to diagnose and solve these issues- not highly interested in putting it in the shop.

Sir’s and ladies... any insight or inquiry would be much appreciated.

 

Even if things are physically connected, there may be corrosion / loose connection not readily visible to the eyes.

1) Start by uncovering ALL suspect connections and make sure you have bare, shiny metal in tight contact with bare, shiny metal.
2) Find a schematic. Sorry I don't have one for your truck but others may have
3) Get a multi-meter. We an help you use it.
I got an $11 DMM from Harbor Freight always in the truck for rough and tumble life - so my nice Fluke stays at home, altho I could easily get by with the $7 one.

 

Sounds like a fusible link gone bad. Check the connection at the battery for corrosion

 

I don't have that schematic in front of me but it's probably like the other years. The critical safety systems, lights horn hazards, are between the FL and one of the primary fuses.