Ok, so this doesnt have to do with stock Mazda parts in general but I thought Id ask here anyway incase someone knows about stereo installation, I bought my FC with an after market Sony 10 Disc CD changer, but the guy sold it to me without the cartridge and I find out the changer is so old they dont make the cartridges anymore, so Im gonna put the CD player from my old car in my FC a Pioneer CD player, anyway me and my friend took the CD player out of my old car and now we took the CD changer out of the trunk (little time consuming not too difficult) and we took the kit out, like the thing that holds the face plate, no I need to switch the wiring harness's but I have no idea how to do this, I see the wires plugging in at the back of the gaping hole where the kit was, also where the stereo kit is are any of the wires in there effecting anything on the dash such as the heater or AC? Any help is needed, thank you in advance

 

there shouldn't be anything directly behind where the stero goes that will affect anything else.

was there already an aftermarket headunit installed in the car? if so and the previous owner used the proper harness adapter for your specific year car then it should be easy to wire that harness adapter into the headunit you are installing.

if a stock stereo was in it then go get the right harness adapter.
might want to check out the audio forum but I also recommend running better speaker wir from the speakers directly to the headunits wiring harness and bypassing all the stock "amps"

good luck, have fun