1978 Dodge Grand Caravan: Some Infinity speakers not working

1978 Dodge Grand Caravan: Some Infinity speakers not working Vehicle has an Infinity system. Radio has been overhauled and tested. Two rear speakers work but nothing from the dash speakers. The two door speakers give a very low volume with a very deep bass and rattle the door but not much else. There are no amplifiers in the speakers, all I see is a small capacitor and a block of epoxy about 3/4"x1/2"x1/2". I presume there is amplifier somewhere but do you have any idea where I might find it?