Sierra 18-99408 Trigger for Mercury 4-Cylinder Outboard Engines

The Sierra 18-99408 trigger is a premium aftermarket replacement ignition component designed for Mercury and Mariner 4-cylinder outboard engines. This trigger works in conjunction with the CDI unit (power pack or switch box) to control ignition timing by sending precise voltage signals to the ignition coils.

How It Works: The trigger features coils that interact with magnets on the flywheel's inner ring. As the magnets pass near the trigger coils, a low-voltage signal is sent to the switch box, instructing the CDI unit when to release high voltage to the ignition coil for spark generation.

Key Features:

• Engineered to meet or exceed OEM specifications
• Designed for harsh marine environments
• Direct replacement for Mercury/Mariner original equipment
• Compatible with 1988-1997 4-cylinder engines: 80 JET, 100, 115, and 125 HP
• Replaces CDI part number 134-9021-4

Replaces OEM Part Numbers: Mercury 99021A2, 99021A6, 99021K2

Sierra products are precision-engineered aftermarket replacements backed by rigorous quality standards, providing reliable performance and durability for marine ignition systems.