Spark Plug Wire Set – Fits Mercruiser 4-Cylinder 2.5L/3.0L (Replaces 816761A5, 84-816761Q5)
Spark Plug Wire Set – Fits Mercruiser 4-Cylinder 2.5L/3.0L (Replaces 816761A5, 84-816761Q5) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Spark Plug Wire Set – Fits Mercruiser 4-Cylinder 2.5L/3.0L (Replace...
Product Details
This Spark Plug Wire Set – Fits Mercruiser 4-Cylinder 2.5L/3.0L (Replaces 816761A5, 84-816761Q5) is designed for Mercruiser 4-cylinder engines, including models 120, 140, 2.5L (153 CID), and 3.0L (181 CID) GM sterndrive motors equipped with conventional points ignition systems (1963–1995).
It serves as a direct replacement for Mercury/Mercruiser part numbers 816761A5, 816761Q5, 84-816761Q5, 84-813720A5, and 84-816761K5, as well as interchanges for Sierra 18-8800-1, OMC 503748, and Mallory 9-28020.
- Engineered for the demanding marine engine environment.
- Includes a complete set of wires with boots, tailored to reach the correct spark plug locations.
- Ensures reliable ignition performance as a direct replacement for conventional systems.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/Mercruiser | 816761A5 |
| Mercury/Mercruiser | 816761Q5 |
| Mercury/Mercruiser | 84-816761Q5 |
| Mercury | 84-813720A5 |
| Mercury | 84-816761K5 |
| Sierra | 18-8800-1 |
| OMC | 503748 |
| Mallory | 9-28020 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercruiser owners: Please verify your model and serial number range to ensure correct fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercruiser | 120 GM 153 I/L4 | 120 | 4-Stroke | 1963–1982 | 816761A5 | Model 6229718-0B531853 |
| Mercruiser | 2.5L GM 153 I/L4 | 120 | 4-Stroke | 1963–1982 | 816761A5 | Model 6229718-0B450800 |
| Mercruiser | 140 GM 181 I/L4 | 140 | 4-Stroke | 1982–1988 | 816761A5 | Model 0B531854-0C856558 |
| Mercruiser | 3.0L GM 181 I/L4 | 140 | 4-Stroke | 1982–1995 | 816761A5 | Model 0B450801-0F353099 |
| Mercruiser | 3.0LX GM 181 I/L4 | 135 | 4-Stroke | 1988–1995 | 816761A5 | Model 0C856559-0F603999 |
Technical Specs
- Product Type
- Spark Plug Wire Set
- Installation
- Direct Replacement
- Fuel Type
- Gasoline
- Connection
- Conventional Points Ignition System
- Housing Color
- Black
- Fitting Type
- Boot-style spark plug end connectors
- Other Technical Attributes
- Complete set with boots at spark plug ends; tailored to reach correct plug locations; designed for marine engine environment
What’s in the Box
- 1 x Complete Spark Plug Wire Set with Boots (816761A5)
Installation Notes
- Disconnect the boat's battery before beginning work.
- Replace one wire at a time to avoid mixing firing order. Note the routing of the old wire from the distributor cap to its corresponding spark plug.
- Gently twist the boot on the spark plug and distributor cap, then pull to remove the old wire.
- Apply a small amount of dielectric grease to the inside of the new wire's boots for a better seal and easier future removal.
- Route the new wire along the original path and press the boots firmly onto the spark plug and distributor cap until they click into place.
- Repeat the process for the remaining cylinders, ensuring each wire is securely connected and properly routed to prevent contact with hot engine parts.
- Once all wires are replaced, reconnect the battery and start the engine to confirm smooth operation.
Troubleshooting & FAQ
How do I know if these spark plug wires fit my engine?
These wires are for specific Mercruiser 4-cylinder engines (2.5L/3.0L) from 1963-1995 using conventional points ignition. To guarantee fitment, check your engine's serial number against the ranges listed in the compatibility table above.
What are signs of failing spark plug wires?
Common symptoms include engine misfires, rough idling, poor acceleration, a noticeable drop in fuel economy, or visible damage such as cracks, burns, or corrosion on the wire insulation and terminals.
How often should I replace my spark plug wires?
While there is no fixed interval, it is best practice to inspect them annually. We recommend replacement every 5-7 years as part of preventative maintenance, or immediately if you observe any signs of wear, damage, or engine performance issues.
Is any special tool required for installation?
No special tools are required, though a spark plug wire puller can make it easier to remove old wires without damaging them or the boots. A small amount of dielectric grease is recommended for the boot interiors.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It's built to OEM-level specifications with comparable materials and manufactured in an ISO 9002 facility, with batch inspections for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
This product is covered by a 1-year warranty against manufacturing defects under normal use. If any issues arise, contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement component, not an original equipment manufacturer (OEM) part.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or quality control.
Payment & Security
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