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Electrical Systems



The charging system’s job is to keep the battery charged so the battery can start the outboard. Depending on the engine model Evinrude and Johnson outboard charging systems can provide from 4 amps to over 40 amps of charging current.

Charging systems can be divided into two categories: Non-regulated and Regulated.

Non- regulated charging system

Alternator stator

Main Electrical Components

Moving a magnet back and forth through a coil of wire creates or induces voltage and current flow in the wire. This is called Alternating Current, or AC, because the current flow changes direction every time the magnet changes direction. And regulated charging system uses flywheel magnets and an alternator stator to produce AC in much the same way.

Moving Magnet

The stator consists of a laminated steel core with wire windings. Its located under the flywheel, close to the magnets in the outer rim of the flywheel. As the flywheel rotates, its magnets move past the stator. When the poles of the magnets align with the bosses on the stator, a magnetic field flows through the stator’s metal core, inducing current flow in the wires wrapped around it.

Alternator Stator

As the magnetic poles move past the stator bosses, the magnetic field induced in the bosses constantly changes. This constantly changing magnetic field produces AC electricity in the wire wrapped around the stator. However, the outboard’s battery, electrical system, and accessories requires current that flows in only one direction. This is called direct current, or DC. So the AC output from the stator has to be changed-or rectified- into DC.

Magnetic FlyWheel around the Stator

A rectifier circuit containing diodes is used to change AC into DC. You can think of a diode as a one-way valve for electricity. Current will only flow through a diode when its anode end is more positive than its cathode end. The cathode end of a diode is identified by a stripe.

A circuit with two diodes arranged like this allows current to flow from the stator to the battery only when the yellow wire is negative, and the yellow/gray wire is positive. When the yellow/gray wire is negative, the two diodes block current flow from the stator to the battery. This circuit is called a half-wave rectifier.


A circuit with four diodes arranged like this allows current to flow from the stator to the battery if either wire is positive or negative. This circuit is called a full-wave rectifier. Notice that when either stator wire is positive, it is connected to the battery’s positive terminal-and when either stator wire is negative, it is connected to the battery’s negative terminal. When the stator’s leads switch polarity, the rectifier’s diodes automatically redirect the current flow to the battery.

Diode Battery and Alternating Stator

This is how a flywheel, stator, and rectifier work together to generate electricity and charge the battery.

Non-regulated system

Now let’s examine the wiring diagram of a typical non-regulated charging system used on many small outboards in the past. Yellow and yellow/gray output leads from the stator supply AC through a terminal strip - to the rectifier. A red output lead from the rectifier supplies DC to the battery through a common battery terminal on the starter solenoid. A gray lead from the terminal strip directs AC from the stator to the tachometer.

Tachometers on most carbureted outboards are powered by the charging system- NOT the ignition system.

Ways to identify a non-regulated system or a regulated system. A good way to identify a non-regulated system is the rectifier. Outboards with this style rectifier have a non-regulated charging system.

Non-Regulated Rectifier

Some 1983 and older V4 and V6 models may have an accessory regulator in addition to a rectifier.

When testing a non-regulated charging system, you should always test the charging output, before checking other system components. To test the output, you must be able to run the engine in a test tank-or on a marine dynamometer- up to approximately 4500 rpm.

To perform the running output test, use an inductive ammeter or you can use a conventional ammeter by disconnecting the rectifier’s red output lead from the terminal’s strip. Connect the ammeter between the red lead and the terminal strip. Run the engine and measure the current output. Compare it with the specifications in the service manual, if the current output readings are within the specifications, the stator and rectifier are functioning properly.


Continue testing the charging system by checking for loose electrical connections. Loose connections can cause damage to the charging system and other electrical components. Next, test the battery as described in the manufacturer’s instructions for the battery or test equipment.

Test the stator if the charging system’s output does not meet specifications. First disconnect the yellow/gray stator leads from the terminal strip. Connect the leads to an ohmmeter. Measure the resistance of the windings as described in the service manual. If the stator is within specifications, test the rectifier. Use a multimeter to test the rectifier diodes, following the procedures in the service manual. To accurately test diodes, most multimeters require a specific scale or switch position. Refer to the meter’s manual for information on how to test diodes with your multimeter.

Regulated Charging System

A regulated charging system - like this 35 amp system used on some larger carbureted outboards- is similar to a non-regulated system.

Regulated Charging System

The major difference is that it has a rectifier/regulator to protect the battery from excessive charging current. Like a non-regulated system, DC flows from the rectifier to the battery. But when the battery reaches full charge, the rectifier/regulator senses it through the red lead, and the regulator directs the charging current to ground. The regulator will allow charging current to flow again when it senses a low charge on the battery. The rectifier/regulator is often located at the top of the engine block. It is set in a water passage to keep it cool. Some smaller outboards have an air-cooled rectifier/regulator. On Evinrudes with direct injection, the rectifier/regulator is incorporated into the Engine Management Module or EMM. Charging systems on Evinrude E-TEC models are covered in other E-ssentials programs.

Rectifier with a purple lead

Some rectifier/regulators are powered by a purple lead. This lead is powered only when the keyswitch is on. Other rectifier/regulators do not have a purple lead and are powered directly by the stator. In some cases, a rectifier/regulator with a purple lead has a service replacement WITHOUT the purple lead

Service Replacement for Purple Lead Rectifiers

In this case, refer to Bulletin number p2001-01. Like the non-regulated system, the first test you perform on a regulated charging system is the Running Output Test. However, you must provide a load to the system before testing its output. Unlike a non-regulated charging system, a rectifier/regulator does not have a continuous output.

Depending upon the charge condition of the battery, output current may or may not be flowing from the rectifier/regulator to the battery when you test the system. You could mistakenly assume the charging system is not working.

Remember- there is no charging current output from a regulated charging system until the rectifier/regulator senses a low battery voltage.

The Cranking Discharge Method

First, we will look at the Cranking Discharge Method: Connect a voltmeter to the outboard´s battery and measure its voltage.


If the battery voltage is 12.5 volts or higher, some energy must be drained from the battery before the charging system can be tested. Disable the engine´s ignition system and crank the engine in short bursts until the battery voltage is less than 12.5 volts with the key in the OFF position.
If you're using an inductive ammeter, you can clamp it around the positive battery cable. For conventional ammeters, disconnect the red output lead between the rectifier/ regulator and the starter solenoid.

Disconnect red output cable

Connect the ammeter in series with the red lead and battery side of the solenoid. Run the engine at 4500 RPM. The ammeter should indicate nearly maximum output from the charging system. As you continue running the engine at 4500 RPM the battery voltage should stabilize around 14.5 volts, and the charging system´s output should begin to decrease. If the engine passes the test, the flywheel, stator, and rectifier/regulator are functioning properly. Check the battery next. Do not use wing nuts for battery cable connections. Hex nuts and star washers are required to securely fasten the battery cables to the battery posts. Check the charging system for loose electrical connections. Loose connections can damage the charging system and other electrical components.

Variable Load Method

Variable Load Tester

The second method for checking the current output of a regulated charging system is the Variable Load Method. This method uses a variable load tester to “load” the battery and make the charging system function. Use an inductive ammeter, or disconnect the red output lead between the rectifier/regulator and the starter solenoid. Connect an ammeter in series with the red lead and the battery side of the solenoid. Connect a variable load tester-or carbon pile resistor- across the battery terminals.

Variable load method

If the tester does not have a built-in voltmeter, connect a voltmeter across the battery terminals. Start the engine. Run it at 4500 RPM. Use the variable load tester to draw the battery down at a rate equivalent to the charging system´s rated output.
The ammeter attached to the outboard should indicate the charging system´s output. Decrease the load on the battery. The ammeter should show reduced charging output. The charging system´s output should approach zero amps as the battery voltage stabililzes around 14.5 volts. If the engine passes the Running Output Test, the flywheel, stator, and rectifier/regulator are functioning properly. Check the battery and wiring connections is a problem persists.

If the regulated charging system does not pass the running output test, the stator must be tested.
Disconnect the stator leads. Check the stator, following the Service Manual. If the stator´s resistance is not within specifications, replace it. There are no tests to check the rectifier/regulator itself. If the charging system´s output is below specifications, and the stator tests okay, the problem most likely is with the rectifier/regulator. In rare cases, the problem may be weak flywheel magnets.

Another feature of the regulated charging system is the tachometer circuit. The AC voltage signal to the tachometer is measured with a peak-reading voltmeter or multimeter that reads frequency in hertz.

Electric Start System

The primary components of an electric start system are:

  • Battery

  • Keyswitch

  • Starter Solenoid

  • Starter motor

  • Neutral safety switch

Electrical System Components

The engine starts when the starter´s motor´s teeth engage the flywheel and crank the engine over. The starter needs high amperage to operate. So the starting system uses a relay called a solenoid, to deliver high amperage to the starter motor.


Let´s see how a solenoid works. Current applied to the small posts on the solenoid flows through a wire coil to ground. This produces a magnetic field, which attracts the plunger and draws it up inside the coil. A metal disc attached to the bottom of the plunger connects the two large posts of the solenoid. Here is how a typical start circuit works. Current travels from the battery to the key switch through a fused circuit.

Starter System Solenoid

When the key is turned to the cranking position, and the control is the neutral position, current flows through the yellow/red lead to the small terminal on the starter solenoid. When the solenoid actuates, the disc electrically connects the two large posts, allowing current to flow through the solenoid to the starter motor.

Battery recommendations vary, depending on the engine size. The battery specifications for each model are printed in the correct Service Manual and in the Operator´s Guide. When troubleshooting an electrical system or installing a battery, make sure you verify that the battery meets or exceeds the specifications. Some boats require more than one battery.

For example: A boat that has an electric trolling motor, or many electrical accessories, may need two batteries- one to start the outboard, and the other to operate the accessories.

Two devices allow the engine to charge more than one battery at a time a battery switch, and a battery isolator.

Battery Switch

The battery switch is used to connect the charging system to the main battery, or to both the main battery and secondary battery. Tell your customer never to turn the battery switch OFF while the engine is running or the charging system can be severely damaged.

Always stop the engine first. The second device used with multi-battery system is a battery isolator. Some models have a built in battery isolator that eliminates the need for an after-market accessory. It is important to understand charging and starter system theory and testing procedures. This will help you to quickly and efficiently diagnose and repair electrical systems.


The outboard electrical system includes the charging system and the starting system.
Charging System:
The charging system can provide from 4 amps to 40 amps of charging current. There are two
types of charging systems: non-regulated and regulated.

**Components of the non-regulated charging system are:
• Flywheel – uses its rim magnets to provide energy to power the stator.
• Alternator stator – coils that generate AC electricity.
• Rectifier – contains the circuitry to change AC electricity to DC electricity.
The major difference between a non-regulated charging system and a regulated charging system
is a rectifier/regulator. The rectifier/regulator is used on the regulated charging system to
protect the battery from excessive charging current.

Starting System:

The electric starting system consists of the following components:
• Battery – stores the DC electricity required for the starting system.
• Key switch – sends electrical signal to the starter solenoid when it is in the cranking position.
• Starter solenoid – allows current to flow from the battery to the starter motor when the
electrical signal from the key switch is received.
• Starter motor – starts the engine when its teeth engage the flywheel.
• Neutral safety switch – prevents the outboard from starting in gear.

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