Does anyone know how to test the headlamp switch in a 65 mustang?

 

Do any of your exterior lights work? They all go through the switch. If none work, check for a blown fuse. If some work but not others, check the bulbs and grounds. All the bulbs have individual grounds. If pairs of lights don't work, like the headlights, or the front parking lights, you might have a switch problem. Certain lights go through the turn signal switch, too. You really should get a wiring diagram or look one up online to do this right. You won't be able to do it without a test light or voltmeter. Wiring problems are some of the hardest to fix so if you have someone that knows how to do it, buy them a pizza and ask for help.

 

Yeah the only lights that work are the turn signals as brake lights.