1999 F 350 with factory cassette radio and speakers

There are 4 speakers in my truck and three do not work.

No matter how I select either fade or balance the sound only comes out of the speaker behind the passenger seat.

Occasionally I can get a small amount of sound from a second speaker but only with the balance set to full on one side and the volume up very high. Is this an audio control card issue inside the radio?
Thanks.
Eric

 

There is no doubt another way to check this, however, with limited equip you could either remove the unit and try switching wires to the one speaker that works and see if the wires to the other speakers are carrying info, OR get another speaker like those in the vehicle and substitute a known good speaker in place of the one(s) presently in each place. tt can be a bit of a problem, but that is what I would try. There is a good possibility the three are questionable.

 

Hanky,
I'll give that a try. Thank you.
Eric