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The electrical connections for a MerCruiser starter motor are made on the solenoid. The solenoid is attached to the top of the starter and sends electrical current to the starter when the ignition switch is turned on. Mercury marine has changed starter and solenoid designs many times over the years. Refer to your documentation for wiring information when replacing original starters and solenoids. Don't be surprised if your replacement unit looks very different than the original one.
Items you will need
Open end wrench set
Open the engine compartment and disconnect the negative lead from the battery with an open end wrench. Locate the starter motor normally at the left rear area of the engine. It is a large cylindrical object with the solenoid attached to the top of it. Examine the solenoid to find the wiring terminals on the rear of it. Draw out a connection diagram on a piece of paper with the terminal placement and wiring color codes.
Connect the large red power lead between the positive battery terminal and the largest stud that has the insulator on it with an open end wrench. The ground connection is made through the starter mounting bracket.
Find the yellow/red wire. This wire is used as the starter switch. Connect this wire to the terminal on the left rear side of the solenoid and terminate the other end to the right terminal on the starter slave solenoid. The starter slave solenoid is located near the carburetor on the right side.
Locate the small red wire. Connect this wire to the terminal between the yellow/red wire and the main power terminal at the back left area of the solenoid. Connect the other end to the small circuit breaker. The wire on the other side of the circuit breaker is the red/purple alternator wire.
Locate the orange wire. This wire is the output wire to the alternator. Connect this wire to the terminal at the top rear of the solenoid. Connect the other end to the terminal located on the right rear of the alternator.
Look to see if there is a purple wire. Some alternators use one, some do not. Connect this wire to the terminal at the right rear of the solenoid. Connect the other end to the yellow/purple wire on the coil.
Check to see if there is a purple/yellow wire. This wire goes to an electric fuel pump and the oil pressure cut-off switch.