Wire connecting alt posts?

I'm installing a new dash wire harness in my 67 Dart GT, aside from needing to solder some pins back into the circuit board, the board looks to be in great shape. Except it has a wire connecting the + and - posts on the alternator gauge(on top of the standard red and black wires). This is my 5th Dart and I've never ran into this before. Any ideas? (I'm also aware that this is probably a simple *** question) By the way the gauge was the only one that worked and was surprisingly accurate