AA Ignition Marine Ignition Coil for MerCruiser GM V6/V8 Thunderbolt IV/V Direct-Fit, Sealed

AA Ignition's marine ignition coil is a direct-fit replacement for select MerCruiser engines, restoring high-voltage spark for reliable starting and smoother running. This coil is designed specifically for inboard marine engines using the Thunderbolt IV & V ignition systems and fits a range of GM V6 and V8 MerCruiser applications. Built with marine-grade materials and sealed against moisture, heat, and vibration, it replaces common OEM numbers such as 18-5438, 392-805570A2, 392-7803A4, 392-805570A1, 72115, and 40511. The unit installs without modification and is backed by a two-year warranty from AA Ignition.

Will this coil fit my MerCruiser engine?

Confirm fit by matching any of the listed part numbers on your original coil or by verifying your engine uses the Thunderbolt IV or V ignition system. This coil is engineered as a direct replacement for MerCruiser GM V6 and GM V8 308 and 350 engines that use those ignition systems.

• Replaces OEM numbers: 18-5438, 392-805570A2, 392-7803A4, 392-805570A1, 72115, 40511
• Compatible with MerCruiser GM V6 and V8 308/350 with Thunderbolt IV & V
• Check stamping on original coil or consult engine service manual for confirmation

How does this coil improve engine performance on the water?

A healthy ignition coil delivers the high-voltage pulse needed for consistent spark at the plugs, which helps reduce hard starting, misfires, and rough idling. Replacing a worn coil returns reliable combustion timing and smoother throttle response, especially under load or in choppy conditions.

• Restores strong spark to eliminate no-start and intermittent misfire issues
• Improves throttle response and smoother idle when paired with good plugs
• Sealed construction resists marine moisture and vibration for stable performance

How straightforward is the installation?

Installation is plug-and-play for compatible engines—no cutting, splicing, or custom brackets required. The coil matches factory mounting points and electrical connections used by the Thunderbolt systems, making it suitable for DIY replacement or quick shop service.

• Direct-fit replacement—uses original mounting and connectors
• Recommended to inspect/replace spark plugs and distributor cap at same time
• Two-year warranty provides added confidence after installation

What quality and warranty can I expect?

This unit is not OEM-branded but is manufactured to meet or exceed factory specifications with marine-grade sealing and finishes. AA Ignition covers the coil with a two-year warranty to protect against manufacturing defects and premature failure.

• Marine-grade materials and sealed against heat, moisture, and vibration
• Engineered to match OEM electrical output and fitment requirements
• 2-year warranty handled through AA Ignition for replacements

Who this is for: If you own a MerCruiser-powered boat that uses the Thunderbolt IV or V ignition system and youre experiencing hard starts, intermittent misfires, weak spark, or rough running, this AA Ignition coil is a cost-effective direct replacement option. It's also suitable for owners who prefer a sealed, marine-grade aftermarket coil that installs quickly and is backed by a two-year warranty. Technically inclined boaters and marine technicians will appreciate the straightforward fitment and OEM-compatible specifications, while owners preparing seasonal maintenance can use this coil as part of a tune-up alongside new spark plugs and ignition components.

FAQ

Q: Does this coil fit MerCruiser Thunderbolt IV and V?

A: Yes. Its a direct replacement for MerCruiser GM V6 and V8 (308/350) engines using Thunderbolt IV and V when part numbers match.

Q: What warranty does AA Ignition offer?

A: AA Ignition provides a two-year warranty covering defects and premature failure; contact support for replacement assistance.