How Does A Bad Rectifier Affect A Motorcycle?

How does a bad rectifier affect a motorcycle? Symptoms can vary from flickering lights to a malfunctioning instrument cluster and even a dead battery.

Most people haven’t heard of motorcycle rectifiers. Yet, despite the lack of attention they get, they’re as vital as the battery or the alternator. They’re responsible for converting AC power into clean, steady DC power, crucial for a healthy battery.

So, how do you know your rectifier has gone bad? And more importantly, how does it affect your motorcycle?

What Is a Motorcycle Regulator Rectifier?

Motorcycle Regulator Rectifier

Before we begin talking about how a bad rectifier affects a motorcycle, we must first understand what a regulator rectifier is.

A regulator rectifier has two key functions: it acts as both a regulator and a rectifier. Rectifiers are circuits that convert AC power to DC power. They’re made of diodes and allow current to flow in one direction only, which is how they convert AC to DC. But what are they doing on a motorcycle?

You see, your motorcycle has what is called an alternator. It’s a generator that produces AC power, which is then used to charge the battery and power your electronics when the engine is on.

The problem is, your battery and your electronics don’t use AC power, at least not most of them. So, it is essential to convert the AC power to DC power first before it is fed to any component damaged by AC power. And that’s where the rectifier comes in.

Okay, but what about the regulator? A voltage regulator is a circuit that’s included with the rectifier. It maintains the DC power from your rectifier at a steady level. Without it, there may be fluctuations, or the DC power may be too high or too low.

As you may have guessed, an issue with the regulator rectifier can be detrimental. At best, it will lower the battery level or cause your lights to flicker. And at worst, it could lead to a dead battery and permanent battery damage.

Why Your Regulator Rectifier Fails – Common Causes:

Why Your Regulator Rectifier Fails - Common Causes

Regulator rectifiers, like other electrical components, are prone to failure. But why do they fail? Understanding the cause of failure will help you narrow down whether your rectifier is failing or not.


One of the most common causes of rectifier failure is overheating. Now, this largely depends on where the rectifier is situated. Ideally, it should be placed away from heat sources such as the alternator or the engine. But on a bike, where space is tight, it’s not uncommon for rectifiers to heat up. Heat will destroy the diodes and melt the connections.


Direct heat isn’t the only thing that melts circuit components. Too much voltage can cause the circuit to overheat and blow out. While a healthy won’t have this issue, it’s common for not properly grounded batteries. And likewise, a fault in your alternator could result in too much current passing through the rectifier.

Shunt Regulator Burnout:

Another common cause for rectifier failure is in the regulator part. The regulator maintains the voltage at a steady level. A failing regulator will provide fluctuating voltage. This is caused by the shunt regulator burning out.

How Does A Bad Rectifier Affect A Motorcycle performance?

Rectifier Affect A Motorcycle performance

Now you know why your rectifier goes bad. But how does a bad rectifier affect a motorcycle? Well, you jumped on the internet to read this article. You tell us!

A bad rectifier won’t show any signs and symptoms, not initially at least. But given enough time, faulty rectifiers will keep your motorcycle from starting.

Regulator rectifiers, in conjunction with the alternator, are crucial for charging the battery. A faulty regulator rectifier will prevent proper battery charging. And while you won’t notice the effects of this immediately, your battery will lose all of its charges with time. This will result in dimmer lights, malfunctioning electronics, and eventually a dead engine.

Exactly how long it will take for that to happen is anyone’s guess. But the more you use the battery, the more you will deplete the charge. So, while a manual charging procedure will restore the battery in most cases, it’s still inefficient to charge the battery every time.

Another thing to consider is that a faulty regulator will mean that your battery receives unclean energy. As a result, the voltage will be fluctuating, which won’t be good for any electrical component. This can damage the battery and any electrical component. The voltage has first to go through before it goes to the battery. And yes, this will most likely lead to long-term damage.

Signs Of a Failed Regulator Rectifier:

A failing regulator rectifier isn’t always apparent. Low battery voltage can be caused by several factors, including a regulator rectifier issue. Here are 8 common symptoms of a failed regulator rectifier:

Higher Voltage Output:

One of the biggest giveaways that your regulator rectifier is faulty is higher voltage output. Since the alternator powers pretty much everything on your vehicle, you can notice this almost instantly.

Higher voltage output means the lights will appear brighter. You may also notice an output spike in your other electronics.

However, this is the best-case scenario. The worst case is that the higher voltage burns out a lot of your electronics. So, your digital displays may stop working. And your head and tail lights may burn out.

This is due to a fault in the regulator. The regulator does not regulate the voltage to a steady level. And so, the electronics are provided with clean and safe energy. It is essential only to try this out when the engine is running. The alternator does not provide power to your vehicle when the engine is off.

Faulty Instrument Cluster:

The instrument cluster is the part on your vehicle which houses the main gauges, meters, and indicators. For example, a motorcycle usually includes a speedometer and gas meters.

When your regulator isn’t working properly, a voltage spike can occur in the equipment. Some parts may handle this well, such as the lights, which will only become brighter. But other parts will ultimately burn out. Depending on how the cluster is built, some components may have an automatic shut-down feature when supplied with too much voltage.

Similarly, a bad rectifier can render the instrument cluster useless. Most clusters, especially the modern ones, are designed to work on DC power. When they are supplied with AC power, the cluster’s output may fluctuate or not show completely. Again, it all depends on the level of protection the cluster has.

Lights That Are Dim or Flickering:

Light flickering

One common symptom of a bad regulator rectifier on a motorcycle is the dimming of the lights. It’s easier to distinguish from other problems in your lights. Since the lights are all connected to the same alternator, they will all be dimming or flickering. If most of your lights are dimming or flickering, you know the regulator rectifier is bad.

This is caused by the battery not getting enough charge. If it doesn’t stay charged, it will slowly lose its voltage, which will cause the lights to dim out.

And since the rectifier isn’t converting the AC power to DC power, the lights will flicker instead of stay on permanently. A bad regulator can also cause this since the voltage level fluctuates instead of staying still.

Dead Battery:

A dead battery is the last sign that your regulator rectifier isn’t working. As the battery doesn’t get sufficient charge, it will start depleting its output voltage. You can try some battery reviving chargers or get a new one.

A dead battery isn’t always caused by a regulator rectifier, though. So, be sure to check the other symptoms as well.

Check Engine or Battery Light:

If the regulator rectifier isn’t working properly, you may be prompted with a Check Engine or Check Battery light. Not all motorcycles have this. But if they do, the light will likely come on.

Now, the light itself is not an indicator that your rectifier is bad. Lots of issues can prompt the light. But if it occurs in conjunction with the other symptoms, it’s surely a clue.

Testing The Regulator Rectifier:

How do you know that your regulator rectifier is the problem? Checking a few symptoms is only the beginning. You need to be extremely sure that the regulator rectifier is malfunctioning. For this, there are a few tests you can perform.

Locating The Regulator Rectifier:

Locate rectifier

Your first goal is to find the regulator rectifier. This is entirely model-specific. Hence, we highly encourage searching online for your exact bike model and where the regulator rectifier can be found. Usually, the regulator and the rectifier are together in one unit. But on some older models, you may find the two as separate units.

Testing The Rectifier:

  • After locating the regulator rectifier, you must first test the rectifier. For this, disconnect all the wires leading into and out of the rectifier. This should go without saying, but turn the engine off.
  • Now, grab your Digital Multimeter (DMM) and set it to the diode testing function. Not all DMMs have this, so you’ll need one with the function.
  • The rectifier is built because it has three terminals that connect to the alternator and two that connect to the battery. So, first, identify the positive and negative terminals on the battery side.
  • Next, connect the negative lead of your DMM to the positive terminal on the battery side. Then, finally, connect the positive lead of your DMM to each of the three prongs on the alternator side one by one. Each prong should read 0.4 to 0.52V on the DMM. Of course, the number can fluctuate, especially if the regulator is faulty. But as long as there’s a number, you can continue with the test.
  • Now, repeat the same process, but swap the multimeter leads. Again, your DMM should give a reading of 0V, which is normal.
  • Next, disconnect all leads, and connect the positive lead of the DMM to the negative terminal on the battery side. Then, connect the DMM’s negative lead to each of the three terminals on the alternator side one by one. If the rectifier is working properly, you should get a reading of 0.4-0.52V. Then, swap the DMM leads, and you should get a reading of 0V.

Testing The Regulator:

  • To test the regulator, you must first connect the regulator rectifier (if you removed it for the rectifier test). Then, turn on the battery. Set your DMM to read DC voltage, setting a suitable range. Connect the negative lead of your DMM to the battery’s negative terminal and the same for the positive side.
  • The voltage reading should fall between 14.5 and 13.5 volts. Any fluctuation beyond that range would indicate a faulty regulator.


How Does a Bad Rectifier Affect a Motorcycle electric system?

A bad regulator rectifier can prove detrimental to your motorcycle. The lights on your motorcycle will either start to dim, become too bright, or flicker. This is the first sign that your rectifier has gone bad.

Other symptoms include a malfunctioning instrument cluster and light burnouts

Eventually, a bad rectifier will keep your battery from charging. And with enough time, it will deplete the battery’s cells down to 0V. And if the regulator is faulty too, it can cause permanent damage to the battery.

Where Is The Regulator Rectifier Located?

Depends on the model of bike you have. Some manufacturers place the regulator rectifier near the radiator. But others may place it near the alternator.

How Do I Test The Regulator?

Testing the regulator is fairly straightforward. First, do not disconnect it from the bike. Instead, place the probes of your multimeter on the two terminals of the battery. Then, check the voltage reading on the multimeter. The voltage reading should be between 13.5 to 14.5V. If not, it should at least not fluctuate. If it does, you know you have a faulty regulator.

How Much Does A Replacement Regulator Rectifier Cost?

Regulator rectifiers are relatively cheap to replace. The price can drop as low as $20. And it can go as high as $100. You may also need to replace or repair any parts that have been damaged due to the bad regulator rectifier.

What Are The Signs Of A Bad Regulator Rectifier?

Initially, you may not notice anything. But eventually, you’ll start seeing the signs. Your lights will start flickering or going dim, and your instrument cluster will show signs of a malfunction. This is caused by your battery running out. Depending on how high the unregulated voltage gets, the lights on your bike might even burn out. You’ll also notice a lower voltage reading on your DMM. Eventually, your engine will completely fail to start.


Most of us don’t realize how vital the rectifier is. Sure, it converts the AC power to DC power. But how does a bad rectifier affect a motorcycle?

In more ways than you may think, especially if your bike is prone to overheating. But luckily, a failing rectifier isn’t too hard to identify. A simple test with a multimeter is enough to tell you whether your regulator rectifier needs replacing or not.

Unfortunately, the problem cannot be solved without a replacement. Good thing rectifiers hardly cost a few bucks. And a new rectifier can last you years on end!