Mercury Outboard Wiring Harness Look at your big plugs and then see if the harness wires turn up, towards the front, or towards the back of the motor. #2770 heads the wires up. #3369 turns to the back. #5532 turns to the front. The Mercury outboard boat harness (external) is at bottom of this chart. Mercury Marine 650 (3 Cylinder) Starter Motor, Starter Parts for Mercury Marine 650 (3 Cylinder) Starter Motor, Starter Solenoid, Rectifier & Wiring Harness.