Audio Systems: Volvo - Pioneer radio/CD, pioneer unit, pioneer radio

Question
1991 Volvo 240, Pioneer DEH1800, 4 speakers already installed, previously had Pioneer unit installed.  Previous unit disconnected with stubs of Pioneer wires still attached to car's wires.  These wire stubs matched exactly my new Pioneer unit's wire colors, so I connected as indicated.  Right two speakers work, left two do not.  Circuit City sales guy told me to bypass factory amp since I have 4 speakers.  I don't know how to do that, nor what the symptom would be if I didn't, but I assume that had been done already since there was a previous Pioneer unit installed with the 4 speakers working.  Before I remove door panels to see if wires detached from speakers, I am asking here for advice.

Answer
Hi Doug,
Amps are only needed if the head unit (like my DEH900RDS) doesn't have any outputs other that RCAs or you really want to P off the neighbors. 4 x 40 output is enough for most people without going deaf.
strip out all amps and wiring and just run the 8 speaker wires to the four speakers directly.
If a speaker is suspect just flash a 1,5v AA battery across the + & - wires to the speaker at the radio end to see if there is a crackle.
Peter