Sounds like the speakers wires may be crossed. Sometimes one crossed ground wire will do that.
A pretty easy way to find out how the speakers are wired in a vehicle is to disconnect the speaker wires from the head unit, grab a 1.5 volt battery, take the grill off the speaker, and hook the speaker leads to the positive and negative on the battery.
If the speaker presses out, the leads are correct.
If the speaker sucks in, they are reversed.
If nothing happens, try another wire.
Write down what goes where, then use the wiring diagram off the head unit to match it up.
[ August 03, 2003, 04:16 PM: Message edited by: Havasu Hangin' ]