If you have a pair of tweeters that you want to install into your car to gain more treble in the music you listen to and don't have an active crossover box, then you can still connect the tweeters to the car speakers in your vehicle, by creating a passive crossover system. A active crossover is the best option for car audio, when installing tweeters because it separates the mid and the high frequencies and only sends the correct frequencies to the appropriate drivers, so you will gain more sound quality along with better sounding clarity. But if you don't have this type of crossover and want to connect them to your car speakers, then you have to protect the tweeter, this is by soldering a small electrical capacitor to the positive terminal, inline with the speaker wire. The capacitor acts as an high pass filter and is there to protect the tweeter's voice coil getting damaged, as the bass frequencies get filtered out.
1) First of all you need to connect speaker wires to both tweeters, this is so you can connect them to each car speaker. So using a pair of 12 or 14 gauge speaker wires, a soldering iron and some solder wire, connect the striped wire to the positive (+) terminal on the tweeter, then the plain black wire to the negative (-) terminal and solder them on, to make the connections secure, to prevent cracking occurring late on. Repeat this step for the other tweeter.
2) Now that you have connected the speaker wires to the tweeters, you are now ready to connect them to your car speakers in your vehicle. So remove the car speaker from its mounted location, this is by removing the front protective grill and then getting an screwdriver and unscrewing all the screws.
3) Then remove the car speaker from the hole and turn it upside, so you can access the terminal connections. Strip the insulation off the wires, if they don't have braid on the ends. Then connect the striped wire to the positiver terminal on the speaker, it will be marked as an (+) symbol. Then connect the plain black wire to the negative terminal on the speaker, it will be marked as an (-) symbol. Repeat this step for the other speaker and tweeter. Once you have made the connections, then test if the tweeters are working, this is by powering on your head unit and playing an random track.
4) If the tweeters are working and are producing sound, then replace the speakers back into there mounting holes carefully and replace all the screws and screw them tight using your screwdriver. Then replace the speaker grills, to protect the cone and rubber surround getting damaged. If the tweeters are not working then check if the speaker wires are damaged and are connected properly onto the terminals on both drivers: tweeter and speaker, before refitting the speaker.