THere is a $6+ switch at Advanced Auto Parts or nearly any other auto parts store for an 1980 Camaro.
It has two nuts where you can adjust it in the bracket to where the brake arm pushes the button in a little when you are not on the peddle.
The switch is not connecting the terminals when the plunger is pushed in a little and the lights will be off. As soon as the peddle moves away from the plunger the terminals will connect turning on the brake lights.
As you push the peddle in and take up the free play in the master cylinder stroke it should turn the lights on.
I have a question on free play on my swinging peddle assm.
Should I put a light spring on the brake arm to keep free play and not let the peddle rest against the master cylinder push rod?
GM used a light spring on manual brake cars only to keep the brake pedal retracted up against the switch. Power brake cars have enough return pressure from the booster diaphragm that the spring is not needed.
I adjust the brake switch so the plunger is pushed all the way in with the brakes off, stepping on the pedal lets the plunger out and the switch contacts close.
With power brakes I mount the booster and where ever the pushrod is at rest is where I put the pedal. Pushrod length can be extended or cut down but on my GM units the pushrod does not come out of the booster (I am talking pushrod attached to the pedal). Dont pull the pushrod out further from the booster, the free play will be built into the booster.