Second trigger on the counsel for line lock. This was in the seventies before I found the T handle switch and I was just out of high school and afraid of the car. I needed both hands on the wheel, eyeballs like saucers and a knot in my gut. I added the radial switch to my post because I thought it was an odd and unusual way of taking care of the problem. At this point the T handle is much better.
Another problem with the clutch trigger I felt for some reason the line lock did not let go immediately when I launched. It was one of those things I couldn't prove but my 60 was better when I did not use it.