I have a 1993 190E with the alpne receiver. The rear spekers and the front door speakers do not work. But the front dash speakers do work. Are those speakers run off of an external amp? Does anyone know what the problem might be?

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1983 240D Yellow
1989 300E Champigne
1993 190E Gray
1986 325 BMW Burgundy
1987 Chevy S10 Blazer