I have a '78 CX and the 7v regulator is inside the gauge cluster housing. I installed a single tach (from a '80 GL I think) in place of the massive gauge cluster on my bike. This new tach only has yellow wire and green wire coming from the bottom side. Looking at my 7v regulator from the '78 I see a yellow, green, and black wire. I know where the yellow ang green go, where does the black one go?