How to Read Outboard Wiring Diagrams

Updated: April 2022 | Category: Resources | Type: Guide / Tutorial

Reading wiring diagrams and troublehooting outboard electrical issues is an essential skill for any lover of powered water craft.

Wiring diagrams, ignition systems and ancillary electrical components are one of most commonly requested content types for download hence we decided to build an archive of Free Outboard Wiring Diagrams but what if you are new to outboard engine electrical systems of have a new outboard with no manual?

This guide teaches you how to read and interpret them so you can make repairs with confidence.

Example of a Coloured Wiring Diagram for the 1984 Johnson V6 engine
johnson 1984 V6 Marine Engine Wiring Diagram
Example Colour Wiring Diagram for 1984 Johnson V6

Wiring Diagrams - Components, Cabling & Layout

There are a huge number of specialist publications availble (see additional resources at the bottom of the page)  but most outboard wiring diagrams are simply a schematic of a series of simple circuits, each consisting of a components, switching and current feed and return cabling.  A small outboard may only have a very simple electrical setup with an ignition circuit and a kill switch, the latter usually being the lanyard.


Larger outboards are more complex, especially those with remote controls, electric starting external supplies for powering ancillaries. Even a mid-size/powered outboard engine around 30Hp or above may have significant complexity.

Mid-size/larger Outboard - Typical Electrical Components might include:

  1. Electronic Ignition,
  2. Lighting Coil,
  3. Rectifier

A wiring diagram is simply a schematic representation of these elements usually roughly laid out aligned to component location in the engine, often aligned to the overhead view of the outboard, i.e. looking down from above it - but not always.

Some owner operator manuals will come with a wiring diagram but almost all service and repair manuals will incorportate one of possible several, depending on complexity.  In addition there are loads of great resources on the web for images or pdf documents to download for outboard wiring diagrams.

Let's explore each element in turn...

Cable Colours & Gauges

Every  wiring diagram will (should!) come with a colour-coded legend or key so you can identify the wires in your engine.  Each manufacturer has their own standards or norms and there are common themes across all outputs that are typical of DC circuits e.g. Red for positive (+) and Black for return (-)

outboard engine wiring cable colours
Outboard cable colours

While cable colours will have a legend or key cable sizes (or gauges) will probably not so for instance the cables the low-tension (ignition circuit and switch) and high-tension (high voltage leads delivering current to the spark plugs) may not appear differnt on the wiring diagram. However once you can identify the components on a diagram they will be easy to locate.

Wiring Chart


Identifying Wiring Diagram Components


Mid-size outboards and above will have an electric starter and a battery. Locating the battery first is a good way to to orient yourself to the supply for the ignition system, through the ignition switch, kill switch and other visual components of the diagram.

Battery component on a wiring diagram
Battery component on a wiring diagram

Starter Motor

Starter motor, usually fed via the starting solution supplied through the supply via the ignition switch.

Find the Starter Motor on a wiring diagram
Starter Motor on a wiring diagram

Switch (One-way)

Basic one-way switch. Could be retractive, of button or plunger e.g. kill switch lanyard.

Identify a Switch on a wiring diagram
Switch on a wiring diagram


A fuse is a electrical fail safe used to provide circuit protection. It's an element designed  typically part of a fuse box containing several fuses in line.

identify fuse on a wiring diagram
identify fuse on a wiring diagram


Any filiment bulb device such as headlights, brakelights, interier illumination, dashboard lamps etc

identify light on a wiring diagram
Identify a light on a wiring diagram


Resistence element e.g. plug heater, cigeratte lighter.

identify heater on a wiring diagram
Heater element on a wiring diagram


Single or Twin horns

Horn on a wiring diagram


A rheostat is a device for measuring and adjusting electrical output based on resistance for example level of fuel in a tank or dashboard illumination

How to identify rheostat on a wiring diagram
How to identify rheostat on a wiring diagram

Solenoid or Relay

A switching device used to control current flow to a component e.g. starter motor or washer wiper mechanism

how to identify solenoid on a wiring diagram


Other Resources

books on how to read outboard wiring diagrams
Specialist publications will prove invaluable for those undertaking more extensive electrical work


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