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Message: <blockquote data-quote="PNW Mike" data-source="post: 1561404" data-attributes="member: 30494">Mach 460 is the Super Sound option in the wiring manual, Premium is the middle tier sound system, and base audio system is, well, the basic one. The CD player was mostly an add-on harness, with (IIRC) some extra wires in the main dash harness and a smaller sub-harness to connect the CD player to the radio.Both the Mach and premium audio systems had an amp buried way down at the bottom of the dash in front of the gear shift area, and it is very similar between the two systems. On the Premium system that amp drives all of the speakers; on the Mach system it only drives the smaller upper speakers in the doors and in the rear deck (or rear sides for the convertible), and thgen passes a pre-amp signal back to the subwoofer amps in the rear. The Mach system has two subwoofer amps behind the rear seat - the larger speakers in the doors and in the rear are subwoofers. Each of the rear subwoofer amps is mono and is wired to drive two of the speakers - one amp drives the front speakers, the other does the rear speakers, and they do this via a Y splice in the speaker wires. This is not how most speakers are typically wired, but it works.The Mach systems use a 6V amp trigger signal vs the usual aftermarket deck that provides 12V. This can cause a speaker pop on turn on sometimes. This is probably the step-down resistor issue you found.The long grey 8 pin (not 10 pin?) is C280 and has the power connections to the radio: battery, ignition, ground, dash illumination, a "radio on" signal to the amps (confusingly labeled radio mute in many diagrams), and with a CD player, a radio on signal to the CD player so it can turn on. This connect is pretty much the same across all three sound systems.For the two black and metal square-ish connectors: The 8 wire one is C284 which is the pre-amp feed to the amps with the amp trigger wire and a ground and is only present on premium and Mach systems. The other is a 6 wire connector, C278, which is the output of the CD player to the original radio, and is only present with a CD player. For an aftermarket radio install, you should be able to remove the CD-player specific wiring sub harness if you want to make some more room behind the dash.The base radio had an additional 8 pin connector, C258, for the speaker outputs. I don't think this is present on the Premium or Mach systems. It's similar to C280, but not identical so things can't be plugged into the wrong places.Metra 70-5510 is the adaptor to connect power, ground, etc. to an aftermarket radio via C280 and send pre-amp feeds to the OEM Premium amp or Mach amps via C284. In my case, the pre-amp connector was super fussy to get plugged in correctly; I don't think it is a super good/robust connector design, but maybe the one in my car got manhandled by a previous owner and/or shop.The Mach amps will work via an aftermarket pre-amp feed, but depending on your goals, you may not end up with the sound quality you want. The OEM speakers are quite old by now and don't have any non-OEM direct replacement that I know of. The Mach system used non-standard speaker ohm values in standard sized speaker mountings. If you want to upgrade your speakers, you may also want to consider moving to an aftermarket amplifier, but that's up to you. The rear subwoofer amps seem to also have a bad habit of not turning off fully and draining your battery, convertibles where they can easily get wet due to top leaks may cause this to happen.Full disclosure - I did a ton of investigation to figure out how to upgrade my '97 after moving to a double din head unit, as it just didn't sound right to me. I eventually just decided to go to an aftermarket 4 channel amp, new speakers all around, and a small powered subwoofer in the trunk. My goal was good sound that I could hear with the top down, not to blow out what's left of my eardrums; your goals may be different. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile    :)" loading="lazy" data-shortname=":)" /> This information is for context so you have it.</blockquote>