Audio Systems: Door Speakers Wont Work, dear victor, mustang mach

Question
Dear Victor,
My brother's car system is a stock system in a 2002 Ford Mustang (Mach System). He has 6 speakers, 2 in the rear, 2 on the door, and 2 on the inside of the window, directly aligned with the outside mirrors. A few months ago, he's been having problems with the door speakers (the ones mounted in the door by your foot). Both the left and right side has stopped working. We know the speakers aren't blown because it's rare for them to blow at the same time. Plus, we tested the wires hooked up to the left side speaker and sound comes out of both the left and right speakers. We recently discovered that both speakers on the left door connect together and then go to the unit. We are assuming that it's the same in the other. We checked the wiring to the unit and it all looks right. The color code is Orange and Green. But what we can't figure out why the top door speakers work and the bottom door speakers don't. Can you help because we're lost and it doesn't make any sense. I wouldn't think that we would need to put another amp in there but I dunno. We don't have an aux amp or sub woofers. It's just a mach set up with a sony unit that we put in ourselves. Thanks for your time

Answer
Hi!
Yeah the top ones are hig frecuency drivers (A.K.A tweeters)so the only thing between the speakers and the tweeters are a little capacitor, if the tweeter sounds but the speaker not i bet the speaker is gone, make an easy test, take a 9v battery (the square ones) and touch the speaker leads, if nothing sounds it's dead. (please desconnect the radio before the test!)