its the resistance against the rod that activates the brake lights. a power brake system will have less resistance and will need a lighter spring than a manual system.
Wow, this is a long thread for just a simple brake light switch. Get a new switch = problem solved. Just get the appropriate one for power or manual.
Installed new switch today. U were right-on Larry! Problem solved. Thanks. Cool temp "mid 60's today - so gud time to crawl under dash - waitin for a day like today. Brake lite comes on if u just barely touch the pedal. I wud/might never have known my brake lites were malfunctioning, if I had not installed the 3rd. lite.