Sierra 18-99400 Mercury Mariner Wiring Harness, Replaces 84-822253A20, Fits 1968-1981 Engines

The Sierra 18-99400 is a boatside wiring harness built for Mercury and Mariner outboard engines, designed to carry the electrical connections between the boat's control side and the outboard powerhead. It is constructed with copper wiring for reliable conductivity and a durable connection under the vibration and moisture exposure typical of marine engine compartments. The harness exits through the side of the lower cowling, matching the routing of the original equipment harness it replaces.

This harness fits 1968-1981 Mercury and Mariner engines that use the 414-2770, 414-3369, and 414-5532 OEM harnesses, and is a direct equivalent for several factory Mercury/Mariner part numbers. It uses a 3.5mm jack connector and measures 11 x 8.5 x 4.5 inches as packaged, weighing 4.2 pounds. Boat owners and marine technicians use this harness to replace a cracked, corroded, or failing original wiring harness without having to source discontinued factory parts.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99400
• UPC: 808282394332
• Weight: 4.2 pounds
• Material: Copper
• Item Dimensions: 11 x 8.5 x 4.5 inches
• Connector Type: 3.5mm Jack
• Harness Exit: Side of lower cowling

Fitment

• Mercury/Mariner engines, 1968-1981, using the 414-2770, 414-3369, or 414-5532 OEM harnesses

Replaces (OEM)

• 84-822253A20
• 84-822253T20
• 45876A10
• 45876A15
• 45876A20

Frequently Asked Questions

What engines does the Sierra 18-99400 wiring harness fit? The 18-99400 fits Mercury and Mariner engines from 1968-1981 that use the 414-2770, 414-3369, or 414-5532 OEM harnesses.

Is the Sierra 18-99400 a direct replacement for the factory Mercury harness? Yes, it replaces OEM Mercury/Mariner part numbers 84-822253A20, 84-822253T20, 45876A10, 45876A15, and 45876A20.

What is the 18-99400 harness made of? This Sierra wiring harness uses copper wiring for reliable electrical conductivity in the marine engine environment.

How much does the 18-99400 wiring harness weigh? The Sierra 18-99400 weighs 4.2 pounds.

What are the dimensions of the Sierra 18-99400 harness? As packaged, the 18-99400 measures 11 x 8.5 x 4.5 inches.

Where does the wiring harness exit the engine cowling? The 18-99400 harness exits through the side of the lower cowling, matching the original equipment routing.

What type of connector does the 18-99400 use? It is equipped with a 3.5mm jack connector.

Will the 18-99400 fit any Mercury outboard regardless of year? No, the 18-99400 is designed for Mercury/Mariner engines built between 1968 and 1981 that use the 414-2770, 414-3369, or 414-5532 OEM harnesses; check your engine's original harness number before ordering.

Why would I need to replace my boat's wiring harness? A wiring harness like the 18-99400 is typically replaced when the original becomes cracked, corroded, or develops intermittent electrical connections from age and marine exposure.

Is this harness sold as a complete boatside unit? Yes, the Sierra 18-99400 is supplied as a complete boatside wiring harness ready to connect between the boat controls and the outboard.