Yup, that's the notch for the Mach 460 tweeters. I don't know how to make the tweeters work without the rest of the Mach 460 system, so I can't help you there. But if your car came with Premium Sound from the factory, you may have some of the Mach 460 wiring in place. Follow the wiring for the door speakers back into the door, and you might find another speaker connector taped up to the wiring harness. For the Mach 460 systems, the plug taped to the harness goes to the door speaker and the plug that was originally on the door speaker goes to the tweeter.