I have the speed wire hooked up and have done the hack for this model and it works, just FYI.
Some harness diagrams want you to view it from the pin side with the wires facing away, other the opposite. pin 18 shows it on the very corner and its yellow. There is only one that's on the corner and yellow (not the fat yellow in that single large pin on the end). I tapped the smaller yellow on the bottom row corner.
PG6speed was nice enough to send me this image for the reverse wire location. When you take the loom off there are two harnesses merged. For me the one closest to the metal interior wall had the orangish tanish wire for reverse. There are 4-5 in there so youll have to test them with a meter. Should read 0 volts in gear/neutral and 11-14 with the car in reverse.
I saw you ask about the bypass on the other post. Here's the info.
Bypass for AVIC-X920BT video.
You can do this or, if you look on the
post on the AVIC411 forum you will see more info. Some guys claim to be able to pull up on the 3 locking tabs on the plug or the AV harness (only to loose it up do not pull it apart) then use staple or 2 or a small object to release that pin. There is a small hole above the hole with the pin itself where the locking tab is. You stick your staple or whatever in the locking tab hole to try and release it (instead of cutting)