Sierra 18-99392 Mercury/Mariner Outboard Wiring Harness, 2/4/6 Cylinder Engines 1966-1981

The Sierra 18-99392 is a wiring harness built to connect Mercury and Mariner outboard engines to the boat's control and instrument wiring. It carries copper conductors terminated with a Mercury/Mariner engine wiring connector, giving a direct plug-in fit at the engine end so the harness routes power and signal wiring between the outboard and the helm without splicing into factory connectors. This harness is sized for a range of Mercury/Mariner outboards spanning 2, 4, and 6 cylinder configurations built between 1966 and 1981, covering horsepower ratings from 20 HP up through 150 HP depending on cylinder count and model year. Copper wiring resists corrosion better than lower-grade conductors and is a standard choice for marine electrical applications exposed to moisture and vibration. Because outboard wiring connectors and pin configurations vary by model year and horsepower, buyers should confirm the harness connector matches their engine's original wiring connector before ordering, or check the manufacturer's recommended part number for their specific application. This harness is intended as a replacement or repair harness where the factory wiring has degraded, corroded, or been damaged, restoring a clean connection between the outboard and the boat's electrical system.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99392
• Category: Mercury Outboard Electrical System
• Material: Copper
• Connector Type: Mercury/Mariner Engine Wiring Connector
• Item Dimensions: 7 x 9 x 2.5 inches
• Weight: 1.2 pounds
• Compatible Engines: 20 and 40 HP (2 cylinder), 50, 65, 80 and 85 HP (4 cylinder), 90, 95, 100, 115, 125, 135, 140 and 150 HP (6 cylinder)
• Compatible Years: 1966-1981
• UPC: 808282394257

Fitment

• Mercury/Mariner 20 and 40 HP, 2 cylinder outboards, 1970-1981
• Mercury/Mariner 50, 65, 80 and 85 HP, 4 cylinder outboards, 1967-1975
• Mercury/Mariner 90, 95, 100, 115, 125, 135, 140 and 150 HP, 6 cylinder outboards, 1966-1979

Frequently Asked Questions

What engines does the Sierra 18-99392 wiring harness fit? The Sierra 18-99392 fits Mercury/Mariner 2, 4, and 6 cylinder outboards, covering 20 and 40 HP (2 cylinder) models from 1970-1981, 50, 65, 80 and 85 HP (4 cylinder) models from 1967-1975, and 90, 95, 100, 115, 125, 135, 140 and 150 HP (6 cylinder) models from 1966-1979.

Is this harness made with copper wiring? Yes, the Sierra 18-99392 wiring harness uses copper conductors, which hold up well against the corrosion and vibration common in marine electrical systems.

What are the dimensions of the 18-99392 harness? The Sierra 18-99392 measures 7 x 9 x 2.5 inches as packaged.

How much does the Sierra 18-99392 wiring harness weigh? It weighs 1.2 pounds.

Does the 18-99392 harness use the original Mercury connector? Yes, the Sierra 18-99392 terminates in a Mercury/Mariner engine wiring connector designed to plug into the factory connection point on compatible outboards.

Will this harness work on any Mercury outboard? No, the Sierra 18-99392 is designed for specific Mercury/Mariner horsepower and cylinder configurations built between 1966 and 1981, so buyers should confirm their engine's horsepower, cylinder count, and model year fall within the listed ranges before ordering.

Why would I need to replace my outboard's wiring harness? A wiring harness like the Sierra 18-99392 is typically replaced when the original harness has corroded, frayed, or been damaged, causing intermittent electrical connections or engine control issues.

Is the Sierra 18-99392 a direct plug-in replacement? Yes, its Mercury/Mariner engine wiring connector is built to connect at the same point as the factory harness on compatible engines, so no splicing into the original wiring is required at the connector.

What is included when I order the 18-99392 harness? The Sierra 18-99392 order includes the complete wiring harness with its Mercury/Mariner engine wiring connector attached.

Can I use this harness on a 6 cylinder Mercury outboard? Yes, the Sierra 18-99392 covers 6 cylinder Mercury/Mariner outboards rated 90, 95, 100, 115, 125, 135, 140 and 150 HP from 1966-1979.

Does horsepower affect which harness connector I need? Yes, connector configuration on Mercury/Mariner outboards varies by horsepower and model year, so it is important to check the manufacturer's recommended part number for your specific engine before installing the 18-99392.