Your post is old, but maybe this info will help someone reading this thread. My 2000 Galant with an Infinity head (MR972458) also has just five wires in the main harness, and the DIN cable to the amp does the rest. According to the shop manual, the wires are:

Pin 4 (Green-White) goes to pin 10 of Junction Block C-74; looks like it is connected to taillight relay, cigarette lighter, license plate light & rheostat.

Pin 9 (Yellow-Black) goes to Joint Connector 2 C-56 & Combination Meter C-30. Seems to be the Memory that you referred to.

Pin 10 (Blue) Goes to Ignition Switch (ACC) that you referred to.

Pin 11 (Red-B(lack?)) goes to Pin 7 of Junction block C-74 through to the Battery.

Pin 12 (Black-Yellow) goes to RHEOSTAT

This is what I can decipher...

Just an update:
http://www.discountcarstereo.com/detail.aspx?ID=434 <- can also be found at Best Buy's Auto Area for a reasonable price. Also, Crutchfield does not offer this item yet (from my experience at least)

I bought a Kenwood KDC-X491 for my 2000 Mitsubishi Montero Sport Limited, and Crutchfield sent me the full harness. Looking at the connector that the harness connects to in the car, only 4 wires on the connector was used - the audio wires and amp power were all on the 6-pin DIN. No audio from it if done this way.. Crutchfield tech support suggested bypassing the Amp by re-wiring everything... but not so! Surfing on the forums quickly (and joining :D) said to grab the DIN adapter above, and hook it to the Male din, and boom, sound was made :D

So, remember to grab that adapter for most Mitsubishi cars it seems!

I completely replaced the amp and head unit on my '99 Galant.

I'll post up pictures in a few minutes for you to see. It really was not very difficult, and in he end I liked it a lot.

update: crutchfield supplies the mitah harness now, included with most HU's. just enter you car's info before buying and it should be in your basket