# 858740T4 Mercury Harness | Genuine Used Part

🔧 Product Description

  

Genuine Mercury Harness Assembly - Part Number: 858740T4

  

A genuine Mercury harness assembly used as an adapter harness in Mercury to Yamaha-style rigging / electrical conversion applications. This harness links compatible Mercury engine or control-system connectors to the matching Yamaha-style connection layout where the 858740T4 harness is specified.

  

⚙️ Key Features

  

• Genuine Mercury harness assembly

• Correct Mercury part number 858740T4

• Adapter harness for Mercury to Yamaha-style connection applications

• OEM Mercury factory harness assembly

• Fitment depends on plug type, engine rigging and control-system layout

  

🔄 Supersession & Cross Reference

  

OEM Supersession Chain:

  

• 858740T4 current / listed Mercury harness assembly reference

  

OEM / Related Numbers:

  

• 858740T4

• 84-858740T4

• 858740

• Mercury to Yamaha adapter harness reference

• Related rigging harness family reference

  

Aftermarket / Verified Equivalents:

  

• No aftermarket equivalent

  

🚤 Compatibility

  

Commonly used on:

  

• Mercury to Yamaha adapter harness installations

  

Typically suits:

  

• Engine / rigging applications:

• Mercury engine installations requiring Yamaha-style adapter connection

• Mercury 14-pin to Yamaha-style rigging conversion applications where 858740T4 is specified

• Mercury remote-control or instrumentation conversion setups using 858740T4

• Mercury / Yamaha shared rigging interface applications matched by plug layout

  

• HP Range: rigging-dependent

• Engine Type: Mercury outboard rigging harness system

• System Type: Adapter harness assembly

• Serial Note: Harness fitment is plug- and rigging-specific. Match by exact engine serial number, control type, connector count and pin layout.

  

🔌 Function

  

The harness adapts electrical control or instrumentation circuits between compatible Mercury and Yamaha-style plug systems.

  

Common signs of failure:

  

• No communication between control harness and engine

• Intermittent gauge or warning function

• Trim, start or key-switch circuit not operating

• Corroded or damaged pins

• Broken wire continuity inside harness

• Fault changes when harness is moved

• Incorrect adapter harness fitted to rigging system

  

📦 Condition

  

• Genuine used part

• Removed from running engine where applicable

• In good working condition unless otherwise stated

## Details

- **Price:** 120.0 AUD
- **Vendor:** Sawley's Auto and Marine
- **Tags:** Sawley’s AAM Used Parts – Electronic Components | ECU CDI & Electrical Parts

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 120.00 AUD | In stock |

## Images

- 858740T4 Mercury Harness | Genuine Used Part
- 858740T4 Mercury Harness | Genuine Used Part

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> Source: [Sawley's Auto and Marine](https://www.sawleysautoandmarine.com.au/products/858740t4-mercury-harness-genuine-used-part)
> Updated: 2026-06-29