I WAS TOLD THERE IS A PURPLE WIRE UNDER DASH IN WIRE HARNESS FOR A TACH. THIS IS FOR A 1993 50HP FORCE MOTOR, IT NEEDS A 12 POLE TACH. I FOUND A PURPLE WIRE COMING OUT OF THE WIRE HARNESS FROM THE ENGINE AND IT GOES DIRECTLY INTO THE IGNITION KEY. IS THIS THE CORRECT WIRE? DO I NEED TO DISCONNECT IT? OR SPLICE INTO IT TO HOOK UP THE TACH?