If you haven't done a "big" stereo installation, it can be a bit confusing until you stare at it for a bit and understand all of the connections. Adding in a seperate aftermarket amp like I did adds even more complexity. When I was thinking through my swap, I found it helpful to write down a list of every connector I was using, then for each connector list out all of the wires in it (with blank spaces noted and if available, pin numbers), the color of each wire, and what each wire is for.
I did a quick lookup on Crutchfield and on the Metra website, and it looks like your '02 radio wiring is different than my '97. It seems '00 was the cutover year to the new style. If you look up a Metra 70-, you can compare it to the connectors behind the factory radio in your dash and see if it matches your connectors. If it does, then that would handle connections at the radio end of things. Some of my notes below are for the earlier style radio connections, but the idea is the same.
But, that doesn't address bypassing the Mach amps, so below is what I learned on my '97, not sure how much of this translates to '02, but some checking of connectors and wiring diagrams may help. The few pictures and info on the front amps that I could find indicates that the front Mach amp look very similar and may have the same connector on yours as on mine, but well, random stuff on the internet is never 100% trustworthy, so you'll want to verify.
When I installed my stereo, my goal was to avoid running completely new wires to the speakers and to avoid cutting and hacking of the factory wiring, so this is written from that perspective - your goals may be different. In my case, I was also able to track down pigtails for the connectors to splice into the Mach subwoofer speaker wiring under the rear seat (to hook up the low frequency speaker outputs from my crossovers) to make it very close to 100% plug and play in terms of the connections I needed to make to the factory wiring. IIRC, the only non-plug and play part was the high power cable I ran from the battery back to the amp. This way, if I ever have to move this to another SN95, it's a pretty easy job.
In my case there was added complexity because I was running an aftermarket amp, but not running a super high powered one, so reusing the factory speaker wiring was a viable option for me. If I was running a larger amp, I would have needed to run new larger wires from the amp to the speakers. My car is a convertible, so I just wanted to be able to clearly hear my music with the top down, not blow what's left of my eardrums out.
For my car, the Mach 460 system used three amps - two woofer/subwoofer amps that drove the large door and rear speakers in mono pairs (each amp drove two speakers and the wires for the pair were literally spliced together in the harness under/behind the rear seat) and a third amp for the remaining four small mids-and-highs speakers (wired in a typical 4 speaker fashion). This third amp is the one is under the dash, buried
way down in front of the gear shift.
I learned that that third amp on mine has the same connector speaker+amp turn on wiring connector as the mid-tier audio system and that it was wired identically in both systems. I mentally modelled this that the two extra Mach 460 amps and wiring are just to drive the larger speakers as big woofers/subs, but that Ford kept pretty much everything else the same and just fed everything above the subwoofer frequencies out of the front amp. Most or all of the Mach 460 wiring seemed to be in seperate harnesses from the main vehicle harnesses, presumably so it could be added on and then just plugged in during assembly based on the desired options.
This understanding of the way the amps were wired ended up being the ah-hah! moment for me, as Metra sells an amp bypass harness for the mid tier system - Metra 70-5605 - that has a nice long set of wires on it that includes an amp trigger wire to run from the dash back to my amp. This Metra adaptor also includes a power wiring adaptor for the radio, but it doesn't include all of the wires I needed in it (IIRC, it didn't have the amp trigger wire unless they're changed it). To avoid this, I used the radio power wire connector from a Metra 70-5510 kit to get all of the wires I needed at the radio.
I powered my aftermarket radio with the grey connector from the Metra 70-5510 kit, and then use the amp bypass connector from the Metra 70-5605 kit to connect to the speaker wires and grab the amp turn on feed at the connector for the third amp under the dash. I ran my pre-amp RCA cables from the radio to my amp in the back and the speaker wires from the Metra 70-5605 connector back to an aftermarket amp under the rear deck (technically, the amp was using this to feed into the wiring under the dash), but you could also tap these directly to the radio speaker outputs to feed the tweeter locations if you were not using a seperate amp.
Keep in mind that on the mach system the speaker wires in the Metra 70-5605 connector (which connects to the connector that originally went into the third/front amp) only feeds an audio signal to the smaller upper component speakers, not the larger woofers. If you wanted to, you could then use a small high/low pass filter and a pigtal of wiring in the doors and at the rear speakers to split the speaker wiring and hook up the lower woofers.
