I mean... does it say "Alpine" on the front speakers? If so, you have a separate amp.

 

No, it is the standard radio.

 

Yes, that diagram shows the same as the one I was looking at, only an antenna amplifier.

 

If you have the wiring diagram, you can test from the radio connector. Any handy test signal.
use an old earphone and connect to your iPhone audio jack. Play your iTunes while testing.
Even a 9v battery may be used to test speakers: connect jumper wires to the appropriate terminals for the speaker that you want to test and brush the other end of the jumper wires across the battery terminals.

As Clubairth1 explained, if speakers failed, repair may be accomplished with a simple solder connection at the terminal strip. However, if the braided copper crumbles when you touch it, replacement speakers may be in order. Good luck, let us know how you resolve the problem.

 

Thanks, a friend of mine mentioned the 9 volt trick to me today. Wish I had known before the put the radio back in!