Electical question

I have a problem with my taillights. When I hit my brake pedal my left turn signal comes(intrament panel) on as well as the drivers side blinkers, front and back. I am thinking this is a short. I want to clean the ground first, but before I do I want to know if I should disconnect my battery. I know this is probably a dumb question, but I have never worked on a car before. I know little about electicity, other than it hurts and it can mess things up if done wrong.

Sorry for the noob question, but it is the only way to learn.

Thanks,
Marc

If you have a trailer plug in unplug it and see what happens