Don't use a Y harness., and, with that radio, you should pretty much try not to have to use a Y harness for anything. 2 batteries to 2 switches to 2 ports. Provides higher current capacity to the Rx and switch redundancy. I had a jet once where I went to fly and neither switch would turn the jet on. So switches do fail. I also killed a couple pairs of Nicads years ago by using a Y harness on the batteries before the switch and they self discharged each other to nothing when I let the airplane sit for a couple months. You might as well also use 22ga wire for servo extensions and such as they will carry the current better.
PS: In the early 70's, I used to fly at the field north of the Beech plant when I was in the Air Force.