1993 Mustang Radio, CD, Wiring HELP

[MustangOwner]

Does anybody know why in a 91 there are 4 rectangle plug ins? Like the plug ins that connect into the back of your radio? My factory tape deck only uses 2 but yet there are 4 harnesses. why? what are the other two for? anybody

 

[Mustang5L5]

https://www.stangnet.com/mustang-fo...emium-sound-stereo-into-87-92-mustang.833958/

Just in case this thread comes up in a search like it did for me