GSMIC400

I've got a 99 gs400 with stock nav/stereo pioneer . I have an aftermarket hu i want to install. I purchased a din plug adapter that doesnt match up .i'm going to use stock amp and speakers. Head unit has 3 separate wire plug. P-1 = 6pin 2 on top 4 bottom. P-2 = 10 pin 4 on top 6 on bottom. P-3 = 8 or 9 pins straight line with only 2 wire going to it.. Ive been searching for the schematic with no luck. Can an newly gs owner get some help.. Thax