6 Symptoms to Detect a Bad Rectifier On Your Outboard

For every boat owner, the outboard motor is a crucial component. You can’t even run the boat when the outboard motor is malfunctioning. And a bad rectifier is one of the main components that make the motor malfunction.

The most common bad rectifier symptoms include battery draining quickly, poor starts, malfunctioning accessories, meter readings fluctuating, and an overcharging battery.

Let’s dive a little deeper to get more insight into the symptoms. We will also discuss the causes of rectifier failure and some advice for preventing future rectifier failures.

What Are the Symptoms of Bad Rectifiers On Outboard?

To learn about a bad rectifier, try looking out for the following symptoms. These 6 symptoms are typically related to an outboard motor’s bad rectifier.

Symptom 1: Battery Drains Very Quickly

A clear sign of a bad rectifier is a battery that drains quickly. It usually happens when the diode has burned out or because of overheating.

Symptom 2: Problems with Starting the Motor

If the outboard motor has trouble starting, that can also mean the rectifier has gone bad. Sometimes you may even face stalling issues, which indicate problems with the rectifier.

Symptom 3: Accessories Start to Malfunction

The malfunctioning boat equipment is another red flag that the rectifier on the outboard motor has failed. These include the ground gauge, wires, spark plugs, impellers, cable grommets, etc. 

Symptom 4: Meter Readings Fluctuate a Lot

Typically, the meter readings you should get from the battery are 12.5 volts. But when the rectifier goes bad, it ruins the voltage transmission, and you will see a lot of voltage fluctuation.

Aside from the multimeter readings, you will also get fluctuating readings on a tachometer. 

Symptom 5: The Battery Tends to Overcharge

Without proper moderation of voltage, a battery can always overcharge. Since a rectifier is responsible for moderating voltage, an overcharged battery can always mean that the rectifier is malfunctioning. You can test the battery using a multimeter.

Symptom 6: Damaged Stator

Stator and rectifier are both closely related and have a direct connection. So, the stator may also sustain damage whenever you have a bad rectifier. 

3 Possible Causes of Rectifier Failure on An Outboard

Usually, the rectifier on your outboard motor is quite strong and durable. However, there are some situations that the regulator rectifiers can’t quite handle. 

The three main causes of your outboard motor’s rectifier failing are listed below.


One of the major reasons for a rectifier to fail is diode burnout. This happens when the rectifier starts to overheat. 

Most of the time a faulty cooling mechanism will result in overheating problems with the rectifier.

Usually, fixing the problem involves replacing the cooling mechanism of your outboard motor. 

If it’s air-cooled, then make sure to get proper airflow on the regulator. If it has water cooling, then you may need to check on the water pump and replace it.

A Damaged Stator

The stator can also cause the rectifier to go bad. because there is a direct connection between these two elements. 

A defective stator can cause a rectifier to fail, but the inverse is also possible.

If you have a damaged stator, replacing it will usually solve the issue. You have to replace it either way because a bad stator causes even more severe problems than a bad rectifier.

Problems with Battery

Sometimes a damaged or a weak battery can be responsible for the rectifier failure. Even a poor battery connection can be the reason for a rectifier failure on your outboard engine. 

Poor grounding can be a prime reason for the rectifier’s failure. In the case of a weak or damaged battery, you have to replace it. 

For other issues, like a worn-out battery connection, you have to fix or replace it. And check the wiring to make sure you have the proper grounding on your outboard.

Replacement And Repair Costs of Outboard Bad Rectifier

Replacement costs vary depending on labor and component costs. Depending on the make and model of your outboard, the cost can go anywhere from $20 to $50 if you can replace it yourself.

However, the price may rise significantly if you choose a professional replacement. 

It’s somewhere between $100 and $200. Repairing it wouldn’t be a good idea because it might start malfunctioning again.

Tips For Maintaining the Outboard Rectifier to Prevent Future Failures

While replacing a rectifier is not expensive, maintenance can prevent it from failing. You can follow the tips we share below for proper maintenance of your outboard rectifier.

  • Go through regular maintenance of your outboard motor.
  • Ensure proper cooling to avoid overheating issues.
  • Check on the battery wiring connections and ground connections.
  • Maintain proper regulations for charging the battery.

In general, these are the easy things you can watch out for to prevent a bad rectifier on your boat’s outboard motor.


Until now, we have discussed all the core parts related to a bad rectifier in an outboard motor. Still, there are some pretty common questions left out. Here we will be answering those to clear out everything.

Does an outboard run without a rectifier?

Yes, an outboard motor should be able to run even without a functioning rectifier. However, it will only last as long as the battery on the outboard is supplying voltage to it. Since the battery won’t charge without a rectifier, the outboard will stop working.

What’s the purpose of a rectifier on an outboard?

The function of a rectifier on an outboard motor is to manage and regulate the voltage. It’s also responsible for charging batteries, taking AC signals and converting them into singular DC signals.

How do you test a rectifier?

You’ll need a multimeter to test a rectifier. Activate the diode function with it. After that, you must take various readings related to the rectifiers. After that, check your battery’s voltage reading to see if it is accurate.

Can you repair a rectifier?

Yes, a rectifier is repairable, but it’s not worth the extra effort. A rectifier for an outboard motor doesn’t cost much. Also, repairing a rectifier requires a lot of expertise and knowledge about the component. So, replacing it is always better.


Finishing it off, we pretty much took you through the whole issue of a bad rectifier in an outboard motor. from the symptoms to the causes and some advice on how to keep them in good condition.

One last tip we can give you is to get the rectifier replaced immediately whenever you notice any of the symptoms. Because the longer it stays bad, the more damage it will cause to the other components of your outboard.

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