Aftermarket Spark Plug Wire Set for MerCruiser 120 and 140 GM Inline 4-Cylinder Stern Drives — 816761A5, 816761Q5, 813720A5, 816761K5
Aftermarket Spark Plug Wire Set for MerCruiser 120 and 140 GM Inline 4-Cylinder Stern Drives — 816761A5, 816761Q5, 813720A5, 816761K5 is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
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Aftermarket Spark Plug Wire Set for MerCruiser 120 and 140 GM Inlin...
Aftermarket Spark Plug Wire Set for MerCruiser 120 and 140 GM Inline 4-Cylinder Stern Drives — 816761A5, 816761Q5, 813720A5, 816761K5 is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket spark plug wire set is designed for selected MerCruiser GM inline 4-cylinder stern-drive applications, including 120 and 140 engines and related 2.5L and 3.0L configurations. Because fitment can vary by engine version and production range, confirm the engine model, year, and serial number before ordering.
Customer-facing reference numbers associated with this wire set include MerCruiser 816761A5, 816761Q5, 813720A5, and 816761K5, along with aftermarket references such as Sierra 18-8833-1, CDI 631-0007, and Mallory 9-28020.
- Designed as a direct replacement for the corresponding original wire set.
- Built with a durable Kevlar core and high-temperature silicone insulation.
- Includes five spark plug wires in application-specific lengths.
Part Number Matrix
Use the following references to compare the wire set with your original part. Part-number references do not replace engine-model and serial-number verification.
| Brand | Part Number |
|---|---|
| MerCruiser | 816761A5 |
| MerCruiser | 816761Q5 |
| MerCruiser | 813720A5 |
| MerCruiser | 816761K5 |
| Sierra | 18-8833-1 |
| CDI | 631-0007 |
| Mallory | 9-28020 |
| OMC | 503748 |
| HeuroFosh | 816761A5 |
Engine and Model Compatibility
The applications below represent listed MerCruiser GM inline 4-cylinder configurations. Always compare the complete engine model and serial number with your original wire set before purchase.
| Brand | Model | Rated HP | Stroke | Years | Reference Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 120 GM 153 I/L4 | 120 | 4-Stroke | 1983–1986 | 816761A5 | Serial range: 6229718–0B531853 |
| MerCruiser | 140 GM 181 I/L4 | 140 | 4-Stroke | 1982–1986 | 816761A5 | Serial range: 6229718–0B450800 |
Technical Specifications
- Product Type
- Marine spark plug wire set
- Application
- Selected MerCruiser GM inline 4-cylinder stern-drive engines
- Installation
- Direct replacement when the original wire configuration and part reference match
- Conductor
- Stainless steel
- Core Material
- Kevlar
- Insulation Material
- Silicone
- Wire Quantity
- 5 wires
- Wire Lengths
- 17.9 in (45.5 cm), 14.2 in (36 cm), 12.1 in (30.7 cm), and 11.6 in (29.5 cm)
- Connector Type
- Spark plug boot
- Temperature Protection
- High-temperature insulation for marine engine-bay conditions
- Package Dimensions
- 10.25 × 7.25 × 2.75 in (260.4 × 184.2 × 69.9 mm)
- Package Weight
- 10.4 oz (0.295 kg)
What's in the Box
The package contains one complete set of five spark plug wires:
- 1 × spark plug wire, 17.9 in (45.5 cm)
- 1 × spark plug wire, 14.2 in (36 cm)
- 2 × spark plug wires, 12.1 in (30.7 cm)
- 1 × spark plug wire, 11.6 in (29.5 cm)
Installation Notes
- Allow the engine to cool completely and disconnect the negative battery terminal.
- Replace one wire at a time so the original firing order and routing are preserved.
- Grip each boot rather than pulling on the wire, twist gently to release the seal, and remove it from the spark plug.
- Disconnect the opposite end from the distributor cap or ignition coil.
- If appropriate for the application, apply a small amount of dielectric grease inside the new boot.
- Route the replacement wire along the original path and press the boot firmly onto the spark plug terminal.
- Connect the opposite end to the matching distributor-cap or coil terminal.
- Repeat for the remaining wires, matching each new wire with the original position and length.
- Reconnect the battery terminal after all wires are installed.
- Start the engine and check for smooth operation, secure connections, and abnormal arcing.
Troubleshooting and FAQ
How do I confirm that this wire set fits my engine?
Compare your engine brand, model, horsepower, stroke, year, serial number, original wire routing, and reference number with the information above. The listed applications are not a substitute for serial-number verification.
Do the wires need to be installed in a specific order?
Yes. Install one wire at a time and connect each replacement to the same spark plug and distributor-cap or coil terminal as the original. Incorrect routing or terminal placement can cause misfiring and poor engine operation.
What are common signs of a failing spark plug wire?
Symptoms may include rough idling, difficult starting, engine misfires under load, poor acceleration, reduced fuel economy, or visible cracks, burns, corrosion, or damage to the wire jacket and boots.
How often should spark plug wires be replaced?
Replacement timing depends on engine use, heat, moisture, and general marine conditions. Inspect the wires during routine maintenance and replace them when damage, deterioration, excessive resistance, or ignition symptoms are found.
What is the benefit of the Kevlar core and silicone insulation?
The Kevlar core supports the wire during installation and operation, while the silicone insulation helps protect against engine-bay heat, moisture, oil exposure, and abrasion.
Is this an OEM part?
This listing is for an aftermarket replacement wire set, not a MerCruiser OEM component. The reference numbers are provided for comparison and identification.
What are the shipping speed and cost?
Typical transit is 5–15 days. Standard shipping is free to most regions, while expedited options appear at checkout where available.
What is the warranty and return policy?
This product is covered by a one-year warranty against manufacturing defects under normal use. Returns are accepted within the applicable standard return period for unused products in their original condition. Contact support for current policy details and return instructions.
Safety and Important Information
- Verify the original wire arrangement, reference number, engine model, year, and serial number before ordering.
- Do not install ignition wires on a hot engine, and disconnect the battery before beginning service.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended when the ignition system or firing order is unfamiliar.
About Sea Sierra
- Pro-Grade Standards: Marine replacement parts selected for demanding real-world conditions.
- Fast Global Fulfillment: Free standard delivery to most regions, with typical transit of 5–15 days.
- Manufacturer-Direct Value: Practical replacement solutions with attention to materials and quality control.
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