Sierra 18-5852 Shrouded Starter Relay, Replaces 821509T01/821509/853292, Fits Mercury/Mariner Four-Stroke 45 HP and 50 HP Outboards

The Sierra 18-5852 is a shrouded starter relay engineered as a direct replacement for the OEM relay on select Mercury and Mariner Four-Stroke outboard engines. The shrouded housing protects the internal contacts and screw terminals from moisture, salt spray, and engine-bay debris, which is critical for a component that lives in the harsh marine environment and controls high-current starter and power trim circuits. It uses a normally-open contact design with copper contacts and screw-type connectors for a secure, corrosion-resistant electrical connection, and it is designed to mount directly to the engine in the factory location.

This relay is built for Four-Stroke Mercury/Mariner 45 HP outboards within the serial number range 0G231123 to 0G472132, and Four-Stroke 50 HP outboards within the serial number range 0G231123 to 0T178499. It replaces Mercury/Mariner relay part numbers 821509T01, 821509, and 853292, so it is a straightforward swap for a failed or corroded factory relay. Sierra engineers its parts to meet or exceed the specifications of the original equipment part being replaced, and every Sierra part is backed by the company's Customer Satisfaction Warranty covering defects in workmanship and materials.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-5852
• Product Name: Relay, Shrouded
• Category: Mercury Outboard Trim Relays
• Connector Type: Screw
• Contact Material: Copper
• Contact Type: Normally Open
• Mounting Type: Engine
• Unit Count: 1
• Weight: 0.6 pounds
• UPC: 808282292546

Fitment

• Mercury/Mariner Four-Stroke 45 HP, Serial Range 0G231123 to 0G472132
• Mercury/Mariner Four-Stroke 50 HP, Serial Range 0G231123 to 0T178499

Replaces (OEM)

• 821509T01
• 821509
• 853292

Frequently Asked Questions

What does the Sierra 18-5852 relay fit? The Sierra 18-5852 shrouded relay fits Mercury/Mariner Four-Stroke 45 HP outboards in the serial number range 0G231123 to 0G472132, and Four-Stroke 50 HP outboards in the serial number range 0G231123 to 0T178499.

What OEM part numbers does the 18-5852 replace? It replaces Mercury/Mariner relay part numbers 821509T01, 821509, and 853292.

Is the 18-5852 relay a genuine Mercury part or an aftermarket equivalent? The 18-5852 is a Sierra-manufactured replacement relay, not a genuine Mercury/Mariner part, but it is built to replace OEM numbers 821509T01, 821509, and 853292 and is engineered to meet or exceed the original part's specifications.

What type of electrical contacts does this relay use? The Sierra 18-5852 uses copper contacts in a normally-open configuration, with screw-type connectors for the wiring terminals.

Why is the relay described as shrouded? The 18-5852 has a shrouded housing that encloses the relay body, protecting the internal contacts and terminals from moisture and debris in the engine compartment, which extends its service life in a marine environment.

How is the 18-5852 relay mounted? This relay uses an engine mounting type, meaning it installs directly onto the outboard engine in the factory relay location.

How much does the Sierra 18-5852 relay weigh? The Sierra 18-5852 shrouded relay weighs 0.6 pounds.

How many relays come in the package? The Sierra 18-5852 ships as a single relay, a unit count of 1.

Will the 18-5852 work on a 40 HP or 60 HP Four-Stroke Mercury outboard? Sierra lists the 18-5852 specifically for Four-Stroke 45 HP (serial range 0G231123 to 0G472132) and 50 HP (serial range 0G231123 to 0T178499) Mercury/Mariner outboards; engines outside these HP ratings or serial ranges are not covered by this listing.

Does the Sierra 18-5852 come with a warranty? Yes, the 18-5852 is covered under Sierra's Customer Satisfaction Warranty, which covers defects in workmanship and materials for the useful life of the product, subject to Sierra's standard warranty terms.

What is the UPC for the Sierra 18-5852 relay? The UPC for the Sierra 18-5852 shrouded relay is 808282292546.