Sierra Trigger 18-99408 for Mercury/Mariner 4 Cylinder Outboards 1988-1997, Replaces 99021A2, 99021A6, 99021K2

The Sierra Trigger 18-99408 is an ignition trigger built to restore reliable spark timing on Mercury and Mariner 4 cylinder outboard engines. The trigger is a core ignition component that signals the engine's control module to fire the spark at the correct point in the crankshaft rotation, and a worn or failing trigger commonly causes hard starting, misfiring, rough idle, or a no-spark condition. Replacing the trigger with the Sierra 18-99408 restores the factory ignition signal path without needing to source a used or salvage part.

This trigger is designed to fit Mercury/Mariner 4 cylinder engines built between 1988 and 1997, covering the 80 JET, 100, 115, and 125 HP models. It is a direct cross to the OEM Mercury numbers 99021A2, 99021A6, and 99021K2, so it installs in place of the original trigger using the factory mounting points and wiring connections.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99408
• Product Type: Ignition Trigger
• Fits: Mercury/Mariner 4 Cylinder Outboards
• Horsepower Coverage: 80 JET, 100, 115, 125 HP
• Model Years: 1988-1997
• Weight: 0.6 pounds
• UPC: 808282394394

Fitment

• Mercury/Mariner 4 cylinder outboards, 1988-1997
• 80 JET, 100, 115 and 125 HP

Replaces (OEM)

• 99021A2
• 99021A6
• 99021K2

Frequently Asked Questions

What engines does the Sierra 18-99408 trigger fit? The Sierra 18-99408 fits Mercury/Mariner 4 cylinder outboard engines built from 1988 to 1997, specifically the 80 JET, 100, 115, and 125 HP models.

Which OEM Mercury part numbers does this trigger replace? The Sierra 18-99408 replaces Mercury OEM numbers 99021A2, 99021A6, and 99021K2.

How much does the Sierra 18-99408 trigger weigh? It weighs 0.6 pounds.

Will this trigger fit a 6 cylinder Mercury outboard? No, the Sierra 18-99408 is designed specifically for Mercury/Mariner 4 cylinder outboards, not 6 cylinder models.

What symptoms indicate the trigger needs to be replaced? Hard starting, misfiring, a rough idle, or a complete loss of spark on a Mercury/Mariner 4 cylinder outboard can indicate the trigger, such as the Sierra 18-99408, has failed.

Is the Sierra 18-99408 a genuine Mercury part or aftermarket? The 18-99408 is an aftermarket trigger manufactured by Sierra, built to replace the OEM Mercury 99021A2, 99021A6, and 99021K2 triggers.

Does the 125 HP Mercury outboard use this trigger? Yes, the 125 HP Mercury/Mariner 4 cylinder outboard (1988-1997) is covered by the Sierra 18-99408 trigger.

What years of Mercury/Mariner outboards use the 18-99408 trigger? Model years 1988 through 1997 for the applicable 4 cylinder Mercury/Mariner outboards use this trigger.

Does the 80 JET model use the same trigger as the 100 HP model? Yes, the Sierra 18-99408 covers both the 80 JET and the 100 HP Mercury/Mariner 4 cylinder outboards, along with the 115 and 125 HP models.

What is the UPC for the Sierra 18-99408 trigger? The UPC for the Sierra 18-99408 Mercury/Mariner trigger is 808282394394.