normaly closed relay?

ok i am going to try and explain what i need for my truck so hear it goes. i need a device that will splice in between a wire that will alow electric current to flow. but when i put electricity to the device it will stop the electric flow. Kinda like a reverse relay. this will be going on an extra brake light i have and i need to turn off the brake light when i flip the switch to run my emergency flashers. I think what i need is a normaly closed relay but i am not sure. i hope i explained that well enough. Can some one tell me what this device is called and where i can get one? I am a retard when it comes to electronics so you will have to tell me the answer as simply as possibol. Thanks for the help guys Tom P.S. I made a very crappy picture of what i need done. i put way to much stuff on my truck

Oh and what ever i need has to be water and weather proof because it will be mounted under my truck bed. Thanks again Tomi put way to much stuff on my truck

thank you very much. i will try this monday and see if it works. And my flasher switch sends a + trigger. Thank you all again.i put way to much stuff on my truck