I have a 93 SC equipped with JBL audio and casette and cd from the factory. I replaced the factory head unit (which had casette only) and swapped the wires on the factory plug so the head unit would have power etc..I retained the cd on the lower console so I would not have a hole there but have no intention of using it. My question is the replacement head unit has CD but it will not play through the existing speakers. Do I have to change the wiring on the factory Ford CD to gain the sound for the replacement head unit?