Just finished the install of the ACC/IG Power Controller and I wanted to share a little tip I learned while doing it: If you have a steering wheel that is adjustable, this install is a piece of cake. Just raise the steering wheel to it's highest setting, shine a light up under the dash, and just look at what the instructions call the "plastic holder with two connectors" under the dash through the space that the moving steering column opened (without yourself being inverted). Since the connectors face the rear of the car, you can clearly see these connectors and locks from this little view port and can easily reach under the dash to manipulate the locking tabs with a small flathead screwdriver while looking through the dash. You may still need to go inverted and crawl under to manipulate the placement of the dongle cables into a spot that you're sure isn't in the way, but you definitely don't have to try to figure out those locking clips or unplug/plug in cables while inverted. Just raise the steering wheel and use the space under the wheel as a view port under the dash.
BONUS: It's so easy to see the locking tab that, at least on mine, I could just remove the C19 connector that the dongle goes onto without having to remove the C-18 connector to get at it. :)
Hope this helps someone else out! Trying to do this inverted was pretty rough and I was so happy to look through the dash and just see the ends of the plugs I was struggling to visualize and manipulate while laying uncomfortably on my back!