Chevy R-10 headlights don’t work

Can anyone help? I just got a 87 Chevy R-10 for my birthday, and there are some wierd things going on. When I first got it, headlights, windows, and radio did not work. Then everything started to work. Now, the radio works, but the headlights and the power windows don’t work. It’s not the switch because the running lights turn on, and it’s not the battery, I fully charged that and it doesn’t work with the car running either. Does anyone know what’s going on?

Do you know how brittle the wire insulation can become in an over 40 year old truck?

Tester

You may have a bad battery cable end. Those side terminal batteries were notorious for hidden corrosion, which often extends under the insulation. I imagine that in addition to the main, thick cable attached to the positive connector there is at least one smaller wire that powers everything but the starter. Check there.