Electrical Schematics Guide - Including 3-and 4-Port Isolation Modules with 2-and 3-Plug Systems and Relay Systems

Oct 25, 2026

Comprehensive electrical reference for trained mechanics focused on diagnosing and repairing WESTERN snowplow electrical systems. Provides schematics, diagrams, and charts for multiple vehicle and plow headlamp configurations, using a headlamp index and harness part numbers to quickly locate the correct wiring schematic. Includes lamp type, wire color, connector identification, component-purpose schematics, and special notes for troubleshooting, while also covering hydraulic system circuitry to present the complete electrical system.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages90

Reading Time3 h 47 min

AccessFree to download

Preface

Introduction

How to Use This Book

Lamp Types and Harness Connectors

Electrical Connectors - 3-Plug Systems

Electrical Connectors - 2-Plug Systems

In-Line Adapter Instructions

Vehicle Harness with Relay

3-Port Isolation Module Systems

Theory of Operation - Overview

Electrical Schematics (3-Plug Variants)

4-Port Isolation Module Systems

Theory of Operation - Overview

Electrical Schematics (4-Port Variants)

Relay System

Wiring and Harness Schematics

Electrical Legend and Wire Colors

SNOWPLOWS November 1, 2008 Lit. No. 22373, Rev. 07 ELECTRICAL SCHEMATICS GUIDE Including 3-and 4-Port Isolation Modules with 2-and 3-Plug Systems and Relay Systems TABLE OF CONTENTS Preface .............................................................................................................. 4 Lamp Types and Harness Connectors.............................................................. 5 Electrical Connectors – 3-Plug Systems........................................................... 6 Electrical Connectors – 2-Plug Systems........................................................... 7 In-Line Adapter Instructions – 28027-2 ............................................................. 8 Vehicle Harness with Relay – 29861................................................................. 9 3-Port Isolation Module Systems ................................................................ 10 Headlamp Index .............................................................................................. 10 Theory of Operation – Overview ..................................................................... 11 Theory of Operation – White Label Non-DRL Module.................................... 12 Theory of Operation – Green Label DRL Module ........................................... 13 Theory of Operation – Blue Label DRL Module.............................................. 14 Electrical Schematic – 3-Plug Straight Blade Snowplows (11-Pin) ................. 15 Electrical Schematic – 3-Plug MVP® Snowplows ........................................... 16 Electrical Schematic – 3-Plug Straight Blade Snowplows with Central Hydraulics ............................................................................. 17 Electrical Schematic – 2-Plug MVP PLUS™ Snowplows (11-Pin) .................. 18 Electrical Schematic – 2-Plug WIDE-OUT™ Snowplows (11-Pin) .................. 19 Headlamp Wiring............................................................................................. 20 4-Port Isolation Module Systems................................................................ 28 Headlamp Index .............................................................................................. 28 Theory of Operation – Overview ..................................................................... 29 4-Port Isolation Module System ...................................................................... 30 4-Port Isolation Module System – Adapter Kits .............................................. 31 Conﬁguration Plug Instructions – 26421 ......................................................... 32 Electrical Schematic – 3-Plug Straight Blade Snowplows (3-Pin) .................. 33 Electrical Schematic – 3-Plug MVP Snowplows (7-Pin) ................................. 34 Electrical Schematic – 2-Plug MVP PLUS Snowplows (11-Pin)...................... 35 Electrical Schematic – 2-Plug WIDE-OUT Snowplows (11-Pin) .....................36 Headlamp Wiring............................................................................................. 37 Relay System ................................................................................................. 47 Relay System – Headlamp Index .................................................................... 47 3 Relay System – Electrical Connectors ............................................................ 49 7-Pin Harness.................................................................................................. 50 Electrical Schematic – 9-Pin Vehicle Harness – Revision 10 and Later.........53 Electrical Schematic – 9-Pin Vehicle Harness – Revision 1–9 .......................54 9-Pin Harness ................................................................................................. 55 Electrical Schematic – 12-Pin Vehicle Harness – Revision 8 and Later ......... 71 Electrical Schematic – 12-Pin Vehicle Harn

FAQs

What is the main purpose of this guide for snowplow electrical systems?

It serves as a comprehensive diagnostic and repair reference for WESTERN snowplow electrical systems, providing schematics, diagrams, and charts to support troubleshooting of vehicle and plow headlamp setups.

How can the correct electrical schematic be located using the book?

Use the Headlamp Index to find the electrical schematic for the vehicle; headlamp harnesses are tagged with the harness part number, which guides you to the relevant diagram.

What additional system information is included beyond headlamp diagnostics?

While focused on headlamp systems, it also includes hydraulic system circuitry so the complete electrical system is covered during troubleshooting and repair.

Oct 25, 2026

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