Brake and turn signal

More than likely you have a short to ground in the brake lighting system.

What we need to do is check for a short to ground on the turn signal circuit when the brake is depressed.

https://www.2carpros.com/articles/how-to-check-wiring

If the turn signal does not work when the brake is pressed and there is no short, then the switch is most likely the issue.

Both the turn signals and the brake lights are run through the switch so I suspect it will prove to be shorted internally.

I am attaching the wiring diagram below which will help with this so please run through this and let us know what you find. Thanks