If your going aftermarket system just have them wire up the output from say the trunk release output to the relay and you can omit the TR7 unit all together. Then when you hit the trunk open it pop the tailgate granted its unlocked already. Just wire the lock and unlock as shown and the tailgate will lock and unlock as you unlock from your remote start fob. As for the function of the single unlock and second click to open all is a feature you will want to tell your installer you want to keep or he will more than likely program the remote system to send a double pulse to unlock the doros then all the doors and tailgate open at once. Now this is also alarm specific so not all have a feature sunctions to allow this type of programing I know most of the newer systems they can do it most installers just chose to go the defualt route. Hope that answers some of the questions.