Finally installed the 3D printed arms for the trimmer attachment and added the Arduino code to control the trimmer motor. Updated on Build 'Instructions.pdf' in the Github project. The 3D printed parts are holding the trimmer motor with zip ties and are locked into place with hex nuts on both sides of the all threaded rod.

The linear actuator attaches to the trimmer motor by using a velcro wrap and the height can then be adjusted with the actuator.

Plus, it makes the trimmer attachment easily interchangeable with the snow plow attachment. As for the wiring I'm using this schematic with a 3rd relay to control the trimmer motor. I also used pin 'A0' on the Arduino for activating the 3rd relay and connected Channel 3 signal cable to D13 on the Arduino. 

So on the "Trimmer Trigger Switch cables" I used  lever connectors, so the trimmer attachment can be switch by only disconnecting 2 cables. I will post another video showing the trimmer attachment working next.