Sierra 18-5815 Starter Solenoid, Black, Replaces Mercury Marine 89-76545, Fits Mercruiser 300 3.4L Serial 5611648 & Up

The Sierra 18-5815 is a black starter solenoid built as a direct replacement for Mercury Marine and Mercruiser engines. It handles the high-current switching duty of relaying battery power to the starter motor when the ignition is engaged, a role that sees repeated heat and vibration exposure in the engine compartment, so a solid factory-fit replacement matters for reliable starts. This solenoid is designed for Mercruiser 300 (3.4L) sterndrive applications with serial number 5611648 and up, and it cross-references directly to Mercury Marine OEM numbers 89-68258A4, 89-853654A1, and 89-76545, so it drops in without modification on engines originally equipped with those parts.

Sierra also offers part 18-5817 for the same application when the setup includes a circuit breaker and fuse; if your original solenoid was paired with those components, 18-5817 is the correct part rather than 18-5815. The 18-5815 measures 7 x 6 x 2.5 inches and weighs 0.61 pounds, making it a compact, straightforward swap for the factory unit.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-5815
• Product Type: Starter Solenoid
• Color: Black
• UPC: 030999320049
• Weight: 0.61 pounds
• Product Dimensions: 7 x 6 x 2.5 inches
• OEM Cross Reference: 89-68258A4, 89-853654A1, 89-76545
• Fitment: Mercury/Mercruiser 300 (3.4L), serial number 5611648 and up
• Related Part: Sierra 18-5817 for circuit breaker and fuse equipped applications

Fitment

• Mercury/Mercruiser 300 (3.4L), serial number 5611648 and up

Replaces (OEM)

• Mercury Marine 89-68258A4
• Mercury Marine 89-853654A1
• Mercury Marine 89-76545

Frequently Asked Questions

What does the Sierra 18-5815 solenoid fit? The Sierra 18-5815 is built for Mercury/Mercruiser 300 (3.4L) sterndrive engines with serial number 5611648 and up.

What OEM part numbers does the 18-5815 replace? Sierra 18-5815 cross-references to Mercury Marine OEM numbers 89-68258A4, 89-853654A1, and 89-76545, so it is a direct swap for engines originally equipped with any of those parts.

Is the 18-5815 the same as the Sierra 18-5817? No. Sierra 18-5815 and 18-5817 cover the same Mercruiser 300 (3.4L) application, but 18-5817 is the correct choice for setups that include a circuit breaker and fuse; 18-5815 does not include that configuration.

What color is the Sierra 18-5815 solenoid? It is finished in black.

How much does the Sierra 18-5815 solenoid weigh? The 18-5815 weighs 0.61 pounds.

What are the dimensions of the Sierra 18-5815? Sierra 18-5815 measures approximately 7 x 6 x 2.5 inches.

Is the Sierra 18-5815 a genuine OEM part or an aftermarket replacement? The 18-5815 is a Sierra-manufactured replacement solenoid engineered to cross-reference and fit in place of Mercury Marine OEM numbers 89-68258A4, 89-853654A1, and 89-76545, rather than a part sold under the Mercury Marine label.

What is included when I order the 18-5815? Ordering Sierra 18-5815 gets you one starter solenoid; no additional wiring or mounting hardware is specified with this part.

Will the 18-5815 work if my old solenoid has a circuit breaker and fuse? For applications that include a circuit breaker and fuse, Sierra specifies part 18-5817 instead of the 18-5815.

Does the Sierra 18-5815 require any modification to install? No modification is indicated; the 18-5815 is designed as a direct-fit replacement for the listed Mercury/Mercruiser 300 (3.4L) application and OEM cross-reference numbers.