Does it have aftermarket fog lights? If the wires for the fog lights are just spliced into the low beams that will over load the relay for the headlights. causiing them to go out and will eventully burn out the relay and the connections on you headlight switch. Also just plain check the relay. Also its not the sub that can give you issues its the amplifer for the system. Anything over 500 watts rms should have at least a 1 farad cap and or a high output alt. Both is the best. Amp draw that isnt properly supported will cause a lot of stress on the whole electrical system but prolly isnt the cause of your problems. Good luck.