Learning how to troubleshoot a motorcycle’s charging system can be one of the more difficult tasks to fully understand. Let’s throw that illusion out, start with a clean slate and learn your motorcycle’s charging system in the most simple and basic way possible.

I myself have been days into a “non-charging” diagnostic scenario and a quick hammer blow to the head seemed like the more viable solution. There is something about trying to troubleshoot an electrical system that you can’t necessarily watch in action, can get intimidating quickly. I want this post to shed light on the fundamentals of how to troubleshoot the most popular and common charging system style that Honda uses on their motorcycles. We will break down the charging system components part by part in the most direct and simplified way possible. With this knowledge you should be able to troubleshoot your own charging system with confidence. Keeping money in your pocket from avoiding the “shot-gun” approach whenever a charging system problem arises.

Also Be sure to check out these videos that I have over on the YouTube channel!

There will be some fundamental explanations throughout this blog, so if your in a hurry to get straight to the testing. Feel free to skip right to my part specific testing videos and explanations by scrolling down ahead. You’re not hurting my feelings!



Etekcity MSR-R500 Digital Multimeter,

Volt Amp Ohm meter with diode and continuity test



aligator clips

Alligator clips help add extra hands to your testing scenario

I use these almost everyday I’m on the job.


 Besides the dog, the test light is a man’s best friend.
I use one like this that gives you a Digital voltage read out.



 Charging Systems Normally Consist of 4 Basic Components.

1. Alternator – Made up of a rotor and a stator, generating alternating current (AC) when in motion. Spins off the revolutions of the crankshaft.
2. Battery – Stores regulated DC current. This needs to be 12.5volts or above for accurate testing results
3. Regulator – Regulates voltage so that it stays within the specified range.
4. Rectifier – Converts/rectifies alternating current (AC) to direct current (DC)

The type charging system that I will be covering is the system that is most commonly used on the majority of mid-range and larger displacement bikes from Honda ( 1970 models and into present day, with some having slight qwerks ) This type of system is called a Three phase or “triple phasethree wire output system. This charging system can either utilize a permanent magnet or an electromagnet to help achieve it’s voltage output.

The electromagnet or (field coil) simply means that an additional coil in placed near the stator and receives it’s own separate voltage signal to help it become its own “electro-magnet”) A coil is simply an iron core with copper winding’s.

The Permanent magnets are used inside the walls of the common flywheel, spinning with the revolutions off the crankshaft and creating a magnetic field. They can also be found in the center of the alternating system like on the older CB750’s
stator and rotor↑ Most common stator and flywheel combination ↑

cb750 stator and rotor   ↑ Older style CB750 combination ↑

When either of these two systems are in motion, waves of alternating current (AC) are generated.ac wave form

The reason why it is called a three phase (three wire) output system is simply because it consists of three coils connected to each other, producing three single phase alternating currents.

Did I loose you?

Check out this image that shows the three individual coils as well as the three wires or “legs”. Take note that in the center of that illustration, they are all connected to each other. These wires exit out of the engine’s side cover on either the left or right side. For Honda, the wires are ALWAYS YELLOW in color.charging system eidted


There are 3 ways you can test a stator


(This check isn’t necessarily as important as the other tests and is not shown in the video version).

• You can do this test by first setting your multi-meter to read AC voltage.

• Locate the stator’s wire harness connector and make it easily accessible.

• Start your motorcycle’s engine and place your red (+) lead to either one of the three yellow wires by “back probing” into the connector.

• Place your meter’s black (-) lead to a solid ground. Do this with all three of the yellow wires.

*Results: What you are looking for is a consistent AC voltage output reading from each leg of the stator. These readings should be closely in range of each other. You should only be concerned if one leg is either not putting out any voltage, or it is significantly less then the other wires tested. In which case the stator has begun to break down or is bad.

2. Check for resistance or continuity through the stator’s windings:

(The bike does not need to be running to do this test)

• Set your multi-meter to the resistance (ohms Ω) setting.

• Disconnect the stator’s wire harness connector.

• Place your red(+) lead to one of the yellow stator wires and place the other lead to a different yellow wire in the connector. You repeat this three times two check all three wires.

*Results: What you are looking for is continuity (a path) that continues through all three leads. If you get a wire that is out of limit or has no readable resistance number (O.L). This more than likely means that there is a break in the windings. You may also get a very high resistance reading. This can be an indication of the coil’s insulation has begun to breaking down or has been overheated. The stator needs to  be replaced.


(most common and easiest test)

• With the stator harness connector still unplugged and your multi-meter still in the resistance (Ω) setting, place your red (+) lead to each of the yellow wires while grounding the black (-) lead to a solid ground.

You will do this test three times on each of the three yellow wires.

*Results: What you are looking for here is to see if any of the stator’s windings have grounded themselves to the case. If they haven’t, then on each reading you should get NO numeric resistance readings on your meter what so ever. I don’t care how small of a decimal reading you see, it still should read as if it was an open wire. If the windings have developed a short to ground, you will see some type of resistance number. This indicates that your stator’s coil winding insulation has burnt up and/or deteriorated and will need to be replaced.

FIY: Because the stator is putting out so much electrical AC energy, the stator is typically the most common FullSizeRendercomponent to either fail or cause other issues down the line. Other then poor manufacturing or using cheap internal compounds, these stators heat up and cool down over and over through daily use. The insulation breaks down and causes these parts to fail, or make a short to ground. Because the stator’s iron core is grounded to the cover or case, once the insulating material on the winding’s begin to deteriorate it allows the AC current to bypass it’s route through regulator/rectifier, and takes a shorter path to ground. Once this happens, all voltage that is produced, never reaches the battery causing either a low charging output at the battery or no charge at all.


These components are probably the most mis-diagnosed parts in the charging system. Almost all reg/rec’s regnow-a-days are combined into one sealed unit. They are not serviceable, and if a problem is found with either systems. The whole unit must be replaced as one. → → →

Pre 1980, some bikes used these two systems as separated units. Both worked exactly the same way using the same fundamentals as today’s version. One other a major change to the early style regulators is that they where able to be serviced and fully adjustable. ↓↓↓regulatorvoltagereg

Regulator Purpose and Function:

Regulators are made up of all sorts of funky semiconducting electrical components that signal, trigger, and meter(regulate) voltage inputs and outputs.

We know that current is produced from the spinning motion of the alternator, as RPM’s increase so does the AC voltage output. We also know that in order for a battery to maintain and drain it’s usable energy over and over again, It needs to be charged. Too much charge can cause overheating, meltdowns, explosions, and fires. To little charge will gradually kill your battery.

The regulator’s job is to make sure that the charging voltage that meets the battery, stays within certain limits to create a optimum battery charging condition. The specific value of this number differentiates from bike to bike.
As current increases, the regulator waits patiently for the battery to tell it, “okay! enough is enough!”. Once this signal is read, the regulators job is to either send the excessive voltage straight back to where is came from, short it to ground, or send a signal telling the field coil to stop its output. Keep in mind that this process is happening faster then you can see.IMG_6623 1



Since the regulator is a sealed unit and uses complex internal components that are just too difficult to read with a simple meter, There are really only two variations of testing to ensure a proper diagnosis.


This is the simplest test you can do before determining if step 2 is required for further testing.

With the bike running at operating temperature.
• Set your meter to read DC voltage.

• Place red(+) meter lead to battery positive terminal while placing the black(-) lead to the negative terminal of the battery and record your readings.

• Now rev the motorcycle’s rpms up to around 3,000rpms and hold. Record your readings.

• Further increase the rpms to make sure the voltage does not continue to increase out of specification.

*Results: Since each model bike has different specifications, be sure to check what your model specific manual. Ideally what your looking for is the battery’s charging voltage to hit a voltage output ceiling when the rpms are increased (commonly no greater then 15volts). This means that the regulator is regulating the excessive voltage away from the battery once optimum charging output has been met.


Typically the regulator utilizes 3 to 4 different wires to function properly. Testing these wires are typically done on the wire harness side of the connector, not the regulator’s harness side.

1.Green wire: Grounds the system to the frame (may have two wires). Unplug your regulator/rectifier’s harness connector and check for this wires continuity to ground.

• Set your meter to Ohms/resistance (Ω).

• Place one lead on the wire and the other lead to a solid ground.

*Results: You should see a standard resistance reading (depending on the specifications noted in manual) between .001 Ω up to .9 Ω. Typically a standard circuit wire has at least .01 Ω of resistance. If you discover that you have and open (no numeric value) or a excessively high reading. Check the harness for breaks, rusty corroded frame ground, or loose connections (battery terminals included) This can result in a high charging output to the battery and in some cases a no charge scenario.

2. Red or red/white wire: Battery voltage (may have two wires). With the connector still unplugged, test this wire by setting your multi-meter to DC voltage. Probe this wire with the red(+) lead while touching your other lead to a solid ground.

*Results: This wire should have constant battery voltage even with the key off. If not, check for breaks in the harness, or loose connections. Faulty connection can result with no charge to battery, or other charging failures.

 3. Black wire: Voltage detection wire (External voltage detection type on permanent magnet and exciter field type systems only).

• Test this wire by setting your meter to DC voltage reading.

• Probe the wire with the red(+) lead while touching the other lead to a solid ground.

• Turn ignition key to the on position.

*Results: Since this wire needs a external signal. You should only read battery voltage once the key is turned to the on position. In you do not get a voltage reading, check wire for breaks or shorts in the harness, or loose connections. Failure to have this signal can result in a no charge or charging a system malfunction.

4. Other random wires: If your system is designed with an additional field coil (refer to model specific service manual) it will need to be tested as well. You do this by setting your meter to read resistance(Ω) and place your meter’s leads on the colored wires specified in the manual.

*Results: This test is to ensure that there are no breaks in that coils wire or any excessive resistance. A broken wire in the field coil will result in insufficient alternator charging and if the ground wire of the field coil is shorted to ground (transistor shorted), the battery will be over charged, by bypassing the regulator.

Get it? Got it? Good….

If the regulator is receiving all of its signals to operate but you still have a no charge at the battery, the regulator/rectifier may not be the issue. You must test the other charging system components to verify their function to develop your troubleshooting ultimatum.


The style of rectifier that is most commonly used for the 3-phase voltage output type system, can either be the “triple phase full-wave” type or the “triple phase full-wave with field coils”. Either way, testing is pretty much the same.

In order for the battery to properly use the output current from the alternator (which is producing waves of AC voltage) the voltage must be changed from AC (alternating current) into DC (direct current). Batteries can not store AC voltage. To accomplish this switch, the rectifier is made up of diodes.

– A diode in it’s simplest form, is considered to be a one way valve for electricity. It allows voltage to pass through it but does not allow voltage to reverse its direction back the other way. Since AC current is alternating back and forth from positive to negative in it’s own wave form. Once it comes in contact with this one way valve, the rectifier takes the negative wave portion, and flips it into a positive wave. This changes the AC wave to a direct (more controlled) voltage signal. IMG_6624


Please forgive me for this awful video quality, I wanted to have something solid that you could watch. I will replace this one soon with a better shot!

For this system, there are only two different series of tests that will give you a total of twelve readings.

TWELVE TESTS?!  Let me explain…. it’s incredibly simple!


Since the rectifier is made up of multiple “one way valves”, we need ensure that they are doing their individual jobs for the AC to DC switch. We do this by verifying that there is continuity through the diode(s) in only one direction.

• Set your multi-meter to read resistance(Ω). Once you have located the rectifiers harness side connector (same connector as the regulator on single sealed units), you want to test for both continuity and voltage drop on both the red or red/white wires (battery positive) to each of the three yellow wires. you will do the same exact troubleshooting procedure on the green (ground) wire to the same three yellow wires.

•The rectifier needs to be unplugged with no voltage running through it. Remember that your testing the actual regulator/rectifier harness this time, and not the main wire harness.

1. Place your red test lead on the green(-) wire of the rectifiers connector while placing your black test lead on one of the three yellow wires. Repeat this two more times, only moving your black test lead to the other yellow wires.

Now switch your meter leads and retest. Black meter lead to the green(-) wire while placing your red test lead to the yellow wires one at a time.

2. Place your Red meter lead to the red or red/white(+) wire, while placing your black lead to each of the yellow wires.

Now reverse your leads and retest in the same manner as before.

*Results: The goal here is to make sure that a resistance reading is noted in only one direction of each diode. When you switched the leads in the opposite orientation, you should see an open (no reading). This outcome needs to be the same on every diode you test. There are six diodes total.

If you get a resistance reading through both ways on the diode. The rectifier is bad and will need to be replaced. Same goes for if you get an open (no numeric reading) through both ends of the diode. The Rectifier is no good, and cannot be fixed.



Battery: This is a huge part of your charging system. This NEEDS to be correctly charged and tested before you start and troubleshooting. A low or failing battery can cause crazy readings during your testing.

If your battery is charging perfectly but your motorcycle still seems to keep killing the battery. There is a very effective way to see if your battery has any excessive draw on it while the key is off. Here is a video explaining this procedure.



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One Reply to “How To Fully Troubleshoot Your Motorcycles Charging system”

  1. […] the key on giving you battery voltage? This post helped a lot of people out maybe have a look? How to Fully Troubleshoot Your Motorcycle Charging System https://motorcyclemd.com/ MotorcycleMD is online now   Quote Quick […]

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