1999 Ford Contour, Radio trouble

I have a 1999 Ford Contour, V6, SE. The Radio lost the two right side speakers, or better said there is no sound from the two right side speakers. It happened slowly. If I raised and lowered the volume while on the right side speakers it would work for awhile. Then nothing...
The Radio is a CD player, single CD, and has an amplifier behind the glove box.
I bought a "used" radio, and a "used" amplifier, and replaced both. Wiring to the door looks good, and the door lock and window work fine (both doors).
So far no luck. Where do I look next?

Phil in Florida Have you tried a "known" good speaker on the right side? Got a great reply from LOSMASTER.

Tried the simple things last and paid the price...

As he suggested, hooked up a speaker (one that works) and checked out the whole shootin match.
I started at the wrong end.

Thanks again. LOSMASTER is da MASTER! Great job

Da Accoustic Master