Go to your local NAPA parts store and pickup a mechanical brake light switch. It has the mounting hardware included.

Mounts inside, out of the weather and the arm of it presses against the brake pedal arm. When the brake pedal is pushed, arm moves and activates a built-in switch which lights up the brakes. Easy wiring, one connection in, one out to lights. Costs about $12 to 15 bucks.

If I find the Part number, I'll post it.