Mercury – Tachometer Harness | Engine Gauge Wiring | 84-69108A5

Overview
This four-pin tachometer harness ties your tach into older Mercury control and wiring setups without any guesswork. It’s built for the classic four-pin plug used across several legacy Mercury harness families. Out on the water, it keeps the tach signal clean so the gauge reads steady instead of wandering. It’s a simple, reliable way to keep older boats wired the way Mercury intended.

Key Features
    • Four-Pin Connector – Matches Mercury’s older tach wiring pattern.
    • Direct Tach Signal Lead – Feeds a clean RPM signal to the gauge.
    • OEM Wire Colors – Uses Mercury’s original wiring layout for easy tracing.
    • Flexible Harness Jacket – Handles vibration and helm movement.
    • Control-Panel Ready – Built for older remote-control systems.

Engine & Boat Compatibility
    • 84-87364A-series harnesses
    • 65640A-series controls
    • 76334A-series controls
    • Four-pin tach circuits

Performance & Practical Benefits
On the water, this harness keeps the tach steady instead of flickering or dropping out when you hit wake or chop. It installs easily—plug it in, route it cleanly, and the tach comes back to life the way it should. It’s a quick fix for older boats where the tach has gone intermittent or stopped reading altogether.

Why Buy OEM
OEM harnesses match Mercury’s wiring standards exactly, so there’s no guessing on pin layout or color codes. They hold up better to heat, moisture, and vibration than generic replacements. It’s the simplest way to keep older control systems reading correctly.

FAQ
1. What are signs the harness is failing?
A jumping tach, dead readings, or intermittent RPM usually point to wiring or connector issues.

2. Does this harness need calibration?
No—just plug it into the correct four-pin connector and the tach reads normally.

3. How does it hold up in saltwater?
It does fine with basic care; keep the connectors clean and lightly protected.

4. Anything important during installation?
Check the control-box terminals for corrosion before plugging in the new harness.

5. What does a worn harness typically do?
You’ll see erratic RPM, flickering readings, or a tach that cuts out when the boat hits bumps.