Audio Systems: Wiring diagram on back of car amplifier is peeling off., rca cables, pitched whine

Question
My husband bought a "new" (to us) car and took his stereo system out of his truck and attempted to install it in the Honda.  Well, the stereo occasionally has a high pitched whine in it, and when that is happening with the radio, the CD player won't play.  It isn't the speakers, because we have checked them, and when it will work right, it sounds good.  Also, the wiring diagram on the back of his ancient, but still sounding great Pyramid Gold Series PB-290 car amplifier has peeled off in places, leaving him only to guess what wire goes where.  Is there anything you can tell me that would help?  I decided to ask someone, since I don't think he ever would.  I would appreciate any help you could give.  I don't think I can stand the quiet car forever.  Thanks.

Answer
If it works at all then the connections to the amp should be fine. I think you have a ground loop problem. What kind/year of Honda is it? Are you using the original deck or an aftermarket deck? Are you using speaker level wiring to the amp or RCA cables? Does the amp run every speaker in the car or just a few?