When Ole Evinrude patented his outboard motor in 1911, outboards were started by yanking on a rope. When people began to tire of spending their energy in yanking the rope, electric starters appeared on outboards. The starter motor replaced the sore muscles, and the solenoid is the relay that controls the starter motor. When you remove your old solenoid and starter, tag the wires with the location from which they came so that when you install the new solenoid and starter, you can put them back on the same posts on the new parts.
Remove the motor cowling. Remove the nut from the negative battery post with a 8 mm (5/16 inch) open-end wrench and remove the ground cable from the post.
Position the solenoid onto the side of the powerhead. Thread the retaining bolts into place and tighten them snugly with a wrench.
Push the yellow/red and black lead (the ground) onto the smaller terminals of the solenoid. Push the two large leads onto the larger terminals on the solenoid and slide the elbow boots over the terminal connections.
Settle the starter motor onto the powerhead. Thread the retaining bolts into place and tighten them snugly with a wrench. If the starter motor has a separate grounding cable, attach it to the motor as well.
Set the yellow power cable from the solenoid onto the terminal on the bottom of the starting motor. Thread the nut onto the terminal and tighten it snugly. Re-install the cowling.