I have a 95 Hyundai Accent. I tried to put a new Pioneer radio into it. I bought adapter plugs that plug together (no chance of mixing up wires). When the unit is turned on it sounds very quiet and very distorted. The speakers are stock, and don't do this with the stock stereo. The radio works fine when plugged into my truck, and my truck radio does the same thing when plugged into the Accent. I have checked the plugs I bought to make sure there wasn't a mistake in production, but found no mistakes. Is it possible that the car's wiring uses a shared ground for the speakers and it is making the new radio malfunction? Any ideas anyone??
I remember way back I had a bunch of trouble with the radio in an Accent. Check the impedance on the speaker wires at the radio - if any of the speakers show something other than 4 ohm that could be your problem.
I don't ever remember having this problem with an Accent, but an Excel I do. The left and right have there own grounds. Test on a DMM for continuity on the grounds to see if they are sharing. If I am correct, these cars simply jumped the grounds together on the harness. Look on the factory harness to see if this is true. If it is, just cut them, if not, you will have to run new wires.