Sierra Trigger 18-99390 for 4 Cylinder Mercury/Mariner Outboards (1976-1997), Replaces 134-6452

The Sierra 18-99390 is a replacement ignition trigger built for 4 cylinder Mercury and Mariner outboard engines produced between 1976 and 1997. The trigger is a core ignition timing component: it generates the signal that tells the ignition module precisely when to fire each cylinder, so a worn, cracked, or intermittently failing trigger is a common cause of misfires, rough idle, hard starting, or a complete no-spark condition on these engines.

This trigger cross-references directly to part number 134-6452, making it straightforward to confirm you are ordering the correct unit for your 4 cylinder Mercury/Mariner powerhead. It is a compact assembly measuring 6 x 6 x 1.75 inches and weighing 0.5 pounds, sized to mount in the same location as the original trigger it replaces, underneath the flywheel on applicable 4 cylinder Mercury and Mariner outboards.

Because ignition timing accuracy directly affects starting reliability, smooth running, and fuel efficiency, replacing a failing trigger with a properly specified unit like the Sierra 18-99390 restores consistent spark timing rather than masking a deeper ignition fault.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99390
• Product Dimensions: 6 x 6 x 1.75 inches
• Weight: 0.5 pounds
• UPC: 808282394233
• OEM Cross Reference: 134-6452
• Engine Application: 4 Cylinder
• Fitment: Mercury/Mariner outboards, 1976-1997

Fitment

• Mercury outboards, 4 Cylinder, 1976-1997
• Mariner outboards, 4 Cylinder, 1976-1997

Replaces (OEM)

• 134-6452

Frequently Asked Questions

What does the Sierra 18-99390 trigger fit? The Sierra 18-99390 trigger fits 4 cylinder Mercury and Mariner outboards built between 1976 and 1997.

Is the Sierra 18-99390 the same as part number 134-6452? Yes, 134-6452 is the cross-reference number for the Sierra 18-99390 trigger, so it installs and functions in place of that number.

How much does this trigger weigh? The Sierra 18-99390 trigger weighs 0.5 pounds.

What are the dimensions of the Sierra 18-99390 trigger? This trigger measures 6 x 6 x 1.75 inches.

Will this trigger work on a 6 or 8 cylinder Mercury outboard? No, the Sierra 18-99390 is built specifically for 4 cylinder Mercury/Mariner outboards from 1976 to 1997, not other cylinder counts.

Does the Sierra 18-99390 fit both Mercury and Mariner outboards? Yes, this trigger fits 4 cylinder Mercury and Mariner outboards built between 1976 and 1997.

What UPC is assigned to this part? The Sierra 18-99390 trigger carries UPC 808282394233.

Is the 18-99390 a genuine Sierra part or a generic aftermarket copy? The 18-99390 is a Sierra-branded replacement trigger that cross-references to OEM/aftermarket number 134-6452.

What does a trigger actually do in the ignition system? A trigger generates the timing signal that tells the ignition module when to fire each cylinder, so a failing trigger like the one replaced by Sierra 18-99390 can cause misfires, hard starting, or no spark.

Can I install the Sierra 18-99390 trigger myself? Replacing the Sierra 18-99390 trigger is a standard ignition component swap that involves removing the flywheel to access the trigger assembly on 4 cylinder Mercury/Mariner outboards.

What do I receive when I order this part? Ordering the Sierra 18-99390 gets you one replacement ignition trigger assembly for 4 cylinder Mercury/Mariner outboards, 1976-1997.