my left brake light on my 95 escort is lighting the wrong filament. it lights up the tail light filament , and when the lights are on, and brakes are applied, neither one work
It could be as simple as a loose bulb. These bulbs have two “button” contacts and a ground. If the bulb is not correctly seated, the paths can cause strange phenomenon.
The bulb could also be bad. For the $1.00 or so that a bulb costs, I’d just replace it as a first step in trying to fix the problem.
Your ground connection to that bulb is bad.