Sierra Premium Marine Spark Plug Wire Set – 47-88021 | MerCruiser Thunderbolt
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You have 30 days to request a return. All sale items are final sale.
Sierra Premium Marine Spark Plug Wire Set – MerCruiser Thunderbolt Ignition
Upgrade your ignition system with this premium spark plug wire set engineered specifically for MerCruiser Thunderbolt ignition applications. Worn or cracked plug wires are a leading cause of misfires, rough idle, and power loss on the water — this Sierra set restores clean, consistent spark delivery with materials built to handle the heat, vibration, and moisture of a marine environment.
Compatible Applications
- MerCruiser engines equipped with Thunderbolt ignition systems
- Refer to Sierra part number 47-88021 application guide for specific engine models and years
Key Features
- Kevlar® core — maximum durability and long service life
- Stainless steel wound conductor — optimized for maximum horsepower and engine performance
- Premium silicone jacketing and boots — high-temperature protection against engine heat
- Superior RFI suppression — protects sensitive onboard electronics from interference
- Corrosion-resistant stainless steel terminals — at both spark plug and distributor ends for maximum conductivity
- OE-style sealed boots — barrier against heat, dirt, and moisture intrusion
- Magnetic suppression core — application-specific design for precise fit
Specifications
- Part Number: 47-88021
- Ignition Type: Thunderbolt (MerCruiser)
- Condition: New
Complete Your Ignition Service
For a full tune-up, pair these wires with a matching distributor cap and rotor. Browse the Ignition Components collection, or consider the Sierra V8 Marine Spark Plug Wire Set – 18-8820-1 or the Sierra MagForce 4-Cylinder MerCruiser 470 Wire Set – 18-8808-2 if you need an alternate fitment.
Parts Desk Insights
This wire set is the right call when a MerCruiser Thunderbolt-equipped engine is showing signs of ignition breakdown — misfiring under load, rough idle at low RPM, or intermittent spark. It’s also a smart preventive replacement during any major tune-up, especially on engines with high hours or several seasons of use. The silicone construction and sealed boots make this set particularly well-suited to bilge-adjacent routing where heat and moisture exposure are highest. Always replace the full set rather than individual wires to ensure consistent resistance across all cylinders.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.