The left blinker was alone in it's own little plug and did a split, the other wire going "somewhere else".. Nothing to do with the mini tach. I would run a separate ground, knowing that it is definitely grounded. The one little wire in the harness for ground is tiny. I had trouble with it making a good connection in that harness plug.
In essence, the left blinker is not in the main wiring harness going to the dash instrumentation. It's a lonely little wire
