The previous set up could have been done 2 ways: 1) Head unit -> amp -> new wires to speakers OR 2) Head unit -> amp -> back to [head unit area] and use the original wires to speakers Option 2 just means you need to remove the head unit and replace the wires coming out of the head unit that go to the amp, and change them so the head unit directly feeds the speakers. Generally the wires you are looking for are white, white/black, grey, grey/black, purple, purple/black and green, green/black out of the head unit. Option 1 means you will need to do the same as option 2, but also reconnect the original wires onto the speakers. If this sounds too complicated, I would suggest going to a car audio shop. I wouldn't pay more than 1-2 hours labour to fix that.