How do you wire a powered subwoofer, like a bazooka?

there is a blue wire you connect off the back of the head unit to amp called remote , it allows the amp to not have power while radio is not in use . You power the amp straight from the battery with a sufficient thickness<guage> red wire . Put an inline fuse on this wire to protect your investment . Then your ground wire is securely fastened to vehicles chassis <or frame if you can >. I always use a huck bolt for that or rivot , bolt and nut will work but stay away from a screw as it can rattle itself loose causing arcing <sparks>. now that the amp is wired for power now you have to get infomation from radio to amp. This is usually done through amp preouts located on back of head unit <radio>. Hook up an rca wire to white and red on back of radio and then plug the other into white and red on amp. That tells the amp when to fire the magnets on the sub and when not too. If your radio has no preouts and can go buy a connector that taps into the rear speakers wires and then the other end accepts the rca wire. Worst case scenario and get help from a knowledgeable guy . and happy listening !!!!!!!!!!!!

RE:

How do you wire a powered subwoofer, like a bazooka?

Does the power have to go to the head unit, or directly to battery? Must both right and left speakers be hooked up. Can I run a wire from existing speakers, leaving them functional, to sub?

In my experience you will need to connect it to our battery and then ground it to your car's chassis.

Then you will need signal (basically always RCA) from the back of your head unit. If you plug it into your rear speaker's wire you will blow it up.