Mercury – SmartTow Engine-to-Helm Harness | 25-Foot Connection Cable | 84-8M0101643

Overview

SmartTow and Cruise rely on a clean, dependable path between the engine and the helm. The Mercury 84-8M0101643 Engine-to-Helm Harness provides that link for mechanical-control MerCruiser gas engines, giving the helm kit the communication it needs to manage towing profiles and steady-speed operation. With this harness in place, the whole system feels more consistent, and the driver can focus on the rider instead of constantly chasing throttle position.

Key Features

• SmartTow Communication Link – Carries the data needed for Cruise and SmartTow features on mechanical engines.
• 25-Foot Length – Provides extended reach for boats with longer rigging runs or aft-mounted helms.
• Mechanical Control Compatibility – Designed for marine-specific MerCruiser gas engines with mechanical throttle and shift.
• Single-Engine Design – Built exclusively for one-engine Cruise/SmartTow applications.
• OEM Plug-In Connectors – Ensures a hassle-free installation with secure factory-style connections.
• Stable Signal Transfer – Maintains clean, reliable communication between the helm kit and engine module.

Engine & Boat Compatibility

• Marine-specific MerCruiser mechanical gas engines
• Single-engine applications
• Boats equipped with Cruise or SmartTow helm kits

Performance & Practical Benefits

This extended-length harness gives drivers the consistent communication SmartTow depends on, especially in boats with more complex rigging routes. With a solid link between the helm and the engine, pull-ups feel smoother, and speed control becomes more predictable—something every tow-sport driver appreciates. The extra length allows for cleaner routing, fewer tight bends, and an overall easier installation in larger runabouts or tow boats. Once routed and secured, the system communicates seamlessly.

Why Buy OEM

SmartTow requires precise signal behavior, and Mercury’s OEM harness is built to match the exact electrical layout of the engine and helm kit. Aftermarket harnesses often introduce false signals or intermittent communication, which leads to inconsistent towing performance. The OEM design maintains clarity, reliability, and long-term durability with factory-correct connectors and shielding.

FAQ

Q1: When would I choose the 25-foot harness instead of the 20-foot version?
If your boat has a longer run from the engine bay to the helm or routing obstacles, the extra length ensures a clean installation.

Q2: Does this harness change throttle feel?
No. It only carries SmartTow and Cruise communication signals and does not alter mechanical throttle behavior.

Q3: Is any programming required after installation?
No. Once connected, the SmartTow system recognizes the harness automatically.

Q4: Can this harness be used on twin-engine boats?
No. It is intended for single-engine applications only.

Q5: Can it handle humid or saltwater environments?
Yes. The connectors and jacket materials are designed for long-term marine exposure.