67 Dart Brake Lights

Hey gents I have a question, so I just picked my first a body, a 1967 Dart GT. She is clean bodied California car, but she has some small issue.
The rear brake lights are stuck on and the gas gauge isn’t working. Now from reading I know the brake light switches can be an issue. But my buddy, who knows a hell of a lot more than me about Mopars, seems to think it’s a ground issue. I have to add that even though my interior is like new I do smell what I think is mouse inside the interior. I’m gonna yank the back seat this week and check out the brake light switch. What else could it be? Should I just replace the rear harness?