"intermittent" brake light

My gf has a 99 blazer. %99.9 of the time her left brake light doesn't work. Once in a while it does. However, The left brake light works %100 of the time if the right turn signal is on. If the left turn signal is on it will also flash as it should. Any ideas?

sounds like the turn signal switch is faulty, this is a modular unit with multiple switches inside, this is a common problem

FCFFUZZYFACE

Would this be the same thing as the "flasher module"? Some one else already said try that. Just wanted another opinion. Is it below the glove box? Thanx.