ullull,
I am not 100% sure if you need to ground the parking brake lead in conjunction with the software mod, but I believe you must.If it is in fact mandatory, I'm sure someone will chime in. Having said that, I finally successfully did it today(mine is the F90, just like yours), and will share with you how:
From what I have read on this forum, you can either do one or the other, hardware mod or software. That being said, in both cases I believe you MUST ground the parking brake (green) lead. If you want to enjoy video while in motion, you cannot hook the parking brake wire to the act