My best guess is broken wires in the door jambs. That will allow the tweeters to work but stop the mids because the wires split upstream of the door jambs.
The wires in the jambs fail due to the doors opening and closing resulting in broken and chafed wires.
With the door open, pinch the rubber boot at one end and then pull it from the door (or jamb, whichever end you're pinching). Then inspect the wires for breaks. The insulation may still be holding the wire together, but the break will be evident - the wire will be flimsy at the break.
If you don't see any breaks on the open end of the boot, then go to the other end, pull it back and inspect there.
On the driver's side, look for gray and tan wires to inspect. On the passenger side, light green and dark green.
The one odd thing about this is that the breaks primarily occur on the driver's door since it gets opened and closed the most thereby flexing those wires the most. So having a broken wire on the passenger side is unusual.
Still, if the tweeters are working, that means the radio is working, which means the failure is further downstream, most likely in the wiring. So inspecting the wiring is the next step.
BTW, these cars are known for failing door speakers. I had to replace both of mine because they had either stopped altogether or were intermittent. So be sure you had everything hooked up properly when you tested the new speakers, just in case it's not the wiring. For example, be sure the harness connectors are fully seated on both ends.
HTH.
Doug
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