The brake lights and tail lights on my 78 280 won't turn off. I don't know if it is a coincidence but while driving just before I noticed the problem I felt something on the floor under foot. It turned out to be some sort of clear plastic plug. Round, clear somewhat soft plastic. Could that have something to do with it?

 

Welcome to ZDriver!

Yep... brake switch... it's located at the top of the brake pedal arm.