Mach 460 Cassete/CD player to 6Disc

Hey, I'm new to the forums so sorry if this is something thats already been covered but I haven't been able to find an answer for myself yet. I have a 99 GT with the Mach 460 single DIN cassette/CD system and I'd like to upgrade to the Dual DIN 6 disc head unit. I know that in order to do this I'll need the other AC radio bezel but my question is will the wiring from my cd/cassette headunits work directly with the 6disc headunit or will I need a harness?? If anybody knows please let me know, I'd really appreciate it!
-Twete

ya I figured the harness would probably be different. so would I need to grab a harness from an 01-03 6 disc unit? and then remove my old harness and solder the new one in place?