I have a 1991 buick regal what do the wires mean for installing a aftermarket cd player?

strange that the wiring harness wouldn't fit, but I can see your concern as you are either going to cut the plug off completely or splice in your wires behind the plug (which is what I would do). As far as knowing what wires are what: - using a digital volt meter or a 12v test light, connect the black wire on the meter or light to a GOOD ground point. Make SURE no wires are loose or touching ground in the radio cavity - turn the ignition to ACC - touch each wire on the radio plug with the red lead off the meter or the pin end of the test light. Make sure to try EVERY wire. - note which wires make the meter measure 12v or the light comes on. those are your power wires - will be at least 1, maybe 2. Since the speakers are not grounded in your system, now find the ground wire in the factory plug as follows: - take the red lead of the meter or wire end of the test light & connect it to one of the known power wires - take the black lead of the meter or pin end of the light & start touching the other wires in the plug one at a time. Again, touch EACH wire. - Note which wire you see the meter say 12v or the light comes on. That is your ground wire. now connect those wires to your new radio & via process of elimination match up the speaker wires on your radio to the ones on the radio plug. Since you've isolated the power & ground wires, shouldn't harm your deck or speakers. once all the speakers are on, the only wire left in the plug should be the power antenna wire. VERIFY it does NOT have 12v at it by using the meter or test light. If it doesn't, connect it to your new radio antenna wire & it should go up.

My guess is that your wiring harness doesn't fit because you're not using the right factory plug. There are three parts to your factory radio system: a small radio control panel, a separate cassette player, and a combined amp/tuner pack buried in the dash under the glove box. There are no speaker wires or antenna connections behind the radio control or the cassette player; you can find the standard GM harness and antenna at the tuner pack.