ohm test or resistance. when i shorted out my corner lights the tailight and interior lights went out also. So do as mention and test the tail light and any other light fuse. Most of the time u can see it visually that the connection broken, but using some sort of tester like a volt meter like what sebba said would be 100 percent. 0 ohms or a beep is what you should expect for connection and or Open symbol or no beep for no connection.

 

Thanks guys, it ended up being the tail lights fuse. The halos had too much power runnin through the circuit