Can you make a dual direction servo run only one way?

[Supermario]

Hey all.
My dump trailer uses a mini servo to lock and unlock the tailgate. My problem is, the Wireless kit I have installed on the trailer only allows me one function which I use for box up and down. I installed a y connector to include the tailgate servo when the box is triggered. When I raise the box the servo unlocks but when I lower the servo moves beyond or to the other side of the lock pin which means when the box comes down it locks but it locks for good! The next time I want to raise it can't open the gate.
What I want is to only run the servo in one direction during box up. When going down it would be in neutral position, the tailgate would not close completely because it would come in contact with the face of the servo arm. Once all the way down all I would have to do is run the box up function for a moment, the arm would get out of the way, the tailgate closes and then locks when up function is stopped.
I thought the red was power in and the black and white were each direction so I made a little jumper and tried only connecting 2 of the 3 wires. In one set up I had barely any movement, tried the other and had nothing.
So rather than run through the rest of the possibilities of which wire where I thought I would ask this long winded question about making a dual action servo a single direction only?

Thanks for any help or input.

Oh, it's a Hitech hs65 servo if that matters.

Mario