I looked for this answer in all the many speaker posts but could not find it. For my 86 GP, I need to replace the rear 4x10 speakers. I have read different things and seen many aftermarket speakers of different impedance values, and all say they will work. But I'm pretty sure they should be matched to the factory radio requirements. So what IS the proper value...4...8...10 ohm? My factory radio still works so I'd hate to burn it up with the wrong speakers. Thanks!