I ran into issues installing an aftermarket stereo into my 2000 LIncoln LS using the subwoofer/center channel amplifier harness provided as part of the Metra 70-5519.
My immediate reaction is that the plug was too big and did not fit even close to properly.
After getting some reassurance from the guys on lincolnvscaddilac, I looked further into the issue.
After removing the red locking plate from the front of the wiring harness clip (the part in the car), i could more easily see where the pins needed to go, and use that same locking plate to bend the Metra harness pins into the right positions.
To remove the red locking plate, I used a flat piece of metal. I inserted into a cavity on each side of the rear edge of the connector, and pressed forward. Eventually it popped loose.
It still does not lock properly, but fits tightly enough it wont' come unseated.
Here are some photos of the alignment/bending of pins using the locking/guide plate.