1981 Chevrolet Custom Deluxe 20 no crank no start, no clicks, but the horn and lights work fine?

A simple experiment:

In the dark, with headlights on, turn the key to start. Do the headlights:

1. Stay bright

2. Dim very slightly

3. Dim a lot or go out?

Basic troubleshooting:

With an automatic transmission in park, or a manual transmission in neutral, momentarily put +12 volts on the starter solenoid terminal (the thin wire goes there). <You can momentarily touch a screwdriver blade from the positive battery cable terminal on the starter solenoid to the solenoid coil terminal.>

What happens?

If nothing happens, you have a problem in the primary starting system: battery, positive battery cable/terminal, negative battery cable/terminal, connections, starter/solenoid.

If the starter turns the engine, you have a problem in the secondary starting (control) system: ignition switch, start relay, fuse, neutral safety switch, wiring, security system.

p.s. I was thinking... There was no start relay or fuse way back in 1981.

Possible bad ignition switch, the horn and lights are on an always hot circuit so they are independent of the ignition switch.

new battery

You can throw parts or you can troubleshoot. Clean the battery posts and the battery terminals. Get a jump, car starts, get the battery charged and load tested. Replace the battery if it fails the load test. No start, check if the starter solenoid has power at both terminals when cranking.

Weak battery, blown relay, blown fusible link, bad starter, dirty and loose cables....or 12 other things.

Weak battery

Bad battery or bad battery connection. Horn and lights working means nothing because it takes more than 10 times more power to start the car than to operate the horn and lights.

Bad fuse or relay somewhere. Unless the lights go dim when the lights are on and you try to start it, then it's the battery. Also try the horn with the lights on, if both work well, look at the fuses etc.

Always clean the battery terminals anyway. See it it jump starts. If so, battery is weak. Check to see it your backup lights work, then check to see if it starts in neutral. Could be the neutral safety switch, which is between the ignition switch and the starter. The reverse lamp switch is part of that safety switch.

Apparently, this doesn't have a relay for the starter.

Sounds like it needs to be taken to the shop for an expensive fix, especially since it was made before modern technology..