95 LS400

Having problems with Nakamichi Speakers. There are times when only the front 2 speaker and the rear right Speaker have any sound and the sub has partial sound but overall still sounds pretty good. The rear Left does not have any sound at all. There are also times when only the front left speaker is the only speaker with sound. Today I checked all of the speakers individually removing the door panels and to my surprise I removed the rear left speaker which never has no sound, I plugged it in another door ad it worker just fine. I’m confused. I was hoping it was the speaker that was bad and I could just replace it, but that was not it.

Please, any assistance will be appreciated.