Starter Solenoids Manufacturer

Premium starter solenoid is one of the main product line in MZW motor manufacturer.


With over 600 selections of solenoids available in our factory, MZW performance starter solenoids are good fit in a wide range of starter motors, from heavy duty to light weight , as well as marine starters.

Every MZW starter solenoid has gone through highly controlled conditions to ensure the high quality of your solenoid switches.


With over 400 selections of solenoids available in our factory, MZW performance starter solenoids are good fit in a wide range of starter motors, from heavy duty to light weight , as well as marine starters.

Every MZW starter solenoid has gone through highly controlled conditions to ensure the high quality of your solenoid switches.

Each MZW starter solenoid is strictly tested with varies of test methods:                        

  • Coil resistance test                   
  • Pull in volt test                   
  • Release volt test                   
  • Volt drop test
  • Pull current test
  • Hold current test
  • Additional travel test
  • Rated current test
  • Current in rush test
Our perfect-quality management system ensures that MZW starter solenoid will meet you and your customers’ expect, each and every time.

Why MZW Starter Solenoid?

We guarantee you every MZW Starter Solenoid has passed a series of strict tests:

MZW Made Starter Solenoid

As a professional automobile starter solenoid manufacturer MZW commits to making quality products.

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MZW Starter Solenoid Guide

starter solenoid

The starter solenoid is one of the main parts of a vehicle starting system. Virtually all modern cars use it, both gasoline and diesel models. The component is so important that an engine will not start if it’s faulty or missing. This guide explains the solenoid in detail, from the starter solenoid definition, working, to how to how it’s wired.

What is a starter solenoid?

Many people do not understand the starter solenoid. Some even confuse it with the starter relay. We will be looking at the differences between the two. For now, let’s see the starter solenoid meaning.

In simple terms, a starter solenoid is the electrical device that activates the starter motor. It acts as a switch to connect the starter motor to the battery, usually after receiving an activating current from the ignition circuit.

A typical starter solenoid comes in the form of a tubular metal housing. Inside the housing is a coil of wire around an iron core, a plunger, and contact plate made of copper. Terminals on one side bring current to the assembly, while the other end protrudes the plunger.

Here is a photo showing a car starter solenoid, the kind you’re likely to find in a small engine vehicle. Notice the cylindrical design, the part that has the terminals, and the other that contains the end of the plunger.

purpose of starter solenoid

Starter Solenoid Location

The location of the starter solenoid depends on the vehicle type. Most cars have it attached to the starter motor, a few away from it but near the transmission. It’s usually the tubular device that you see bolted to the top of the motor’s housing

Starter motor mounted solenoids serve the purpose of both an actuator and switch. When mounted away from the motor, the solenoid only acts as a switch. The functions of starter solenoids are explained next.

Starter Solenoid Function

In the modern vehicle, a starter solenoid serves an important role. Here is why.

The engine, whether diesel or gasoline, cannot start on its own. It requires an outside force to initiate the first RPMs. Usually, the starter motor is the component that is tasked with cranking up the engine.

But the motor requires a very large current to work. If the ignition switch circuit circuit were to provide it, its contacts and cables would burn off. Thick wires could be installed, of course. However, that would mean the need for extra space, which would be impractical in most applications.

To avoid all those inconveniences, a starter solenoid is used. It acts as a heavy-duty switch, completing a large-current circuit using a few amps. It also isolates the delicate section of the starting system or ignition circuit.

Those are not the only starter solenoid roles in a car. The device also moves a plunger, causing the starter pinion gear to engage the engine’s flywheel ring gear (or flexplate). In summary, the three starter solenoid functions are:

1. To isolate and protect the ignition key circuit from the battery’s high current.

2. To switch on the starter motor circuit and cause it to start spinning

3. To push a plunger and move the starter pinion gear toward the flywheel (only in starter motor mounted solenoids)

These functions are necessary for the engine to start. But how do they happen? Let us now look inside the starter solenoid, how it works, and several other essential facts.

starter solenoid working principle

How Does a Starter Solenoid Work?

Starter solenoids come in different sizes, designs, and power rating. Despite that, their working mechanism does not change. The parts involved in their operation, too. Here, we are talking about modern version of the device, which may differ in some ways from the traditional models.

Here is how a starter solenoid works in most cars today.

  • When you switch on the engine (by turning a key or pressing a button), current flows to energize a small starter relay. The relay closes contacts to cause a larger current in the starter solenoid. (Some car starting systems have the ignition switch activating the starter solenoid directly.
  • The energized solenoid coil creates a magnetic flux, and the resulting force moves a plunger. The plunger pushes a shift lever, which is part of the linkages that thrust the starter gear to mesh with that of the flywheel.
  • Meanwhile, the moving plunger closes contacts, and current flows from the battery directly to the starter motor. The motor comes into life, rotating the drive shaft and, therefore, the flywheel. That, in turn, rotates the engine crankshaft or transmission.
  • The part of the coil windings that pulls in the plunger is also de-energized, and its current now goes to the motor. This ensures the pull-in coil does not overheat from the high current passing through it. Also, that battery power is not wasted.
  • As soon as the ignition key is released (and the engine has started), current ceases to flow in the solenoid. The coil loses magnetism, and no force holds the plunger anymore. That causes a tension spring to pull it back to its former position. The starter solenoid has now done its work and performed its three functions.

The above events happen almost instantly, resulting in the spin of both the motor and engine. To help you fully understand the starter solenoid operation, let us now look at the major components the make up the device. Below is a cut-away image of the starter solenoid. It shows the parts we will discuss.

starter solenoid parts

Main Starter Solenoid Parts

A typical starter motor solenoid consists of five essential parts. As we have seen, these work to activate the starter motor, actuate the shift lever, and protect the ignition switch circuit. The components are:

1. Starter Solenoid Coils

The coils provide force to move a plunger and retain it once moved. When current flows through the coils, a magnetic field is generated. The resulting magnetic force causes the plunger to make a linear movement inside the solenoids cylindrical housing. A typical starter solenoid has two wire windings, pull-in and retaining or hold-in coils. These are explained below.

Pull in coil- this coil only provides the force to push the plunger. Because it has to overcome the action of the tension spring, the coil carries more amperes than the hold in coil. It also features thicker wires to prevent overheating and power loss. The pull in coil does not operate for long. As soon as the motor starts to spin, its circuit disconnects, leaving the other coil to keep the plunger in the “pull” position.

Hold in coil- located just next to the pull-in coil, the hold-in coil retains the plunger in position until you release the starter key. It carries a much smaller amount of current and serves two purposes. Fist, it prevents current overload by taking over from the large-current pull in coil. Secondly, it reduces unnecessary strain on the battery and conserves the much needed power.

The starter solenoid coils are important parts of the device. If they short or burn out, the solenoid cannot operate anymore, or the power will be too low to be of any use. Most starter solenoid problems are coil issues caused by corrosion or excessive currents burning the wires.

2. Starter Solenoid Cap/Disc

This is the part that allows the completion of circuits to power the device. It contains the starter solenoid terminals. The central terminal is the starter solenoid control wire, with the other two serving as battery positive and starter motor connectors.

Because it holds the starter solenoid contacts, the cap is an important part of the solenoid. Melted or loose connections can cause problems in this part of the starter solenoid. Also, corroded or loose terminals. If the connections are wired wrongly, it can mean a non-functioning solenoid.

3. Starter Solenoid Plunger

The plunger is the part that moves under the influence of the coil’s magnetic field. It connects to a lever, working the linkages that move the starter gear to engage the flywheel. The plunger has to allow a strong force. For that reason, it is usually made from iron. This material produces a strong magnetic attraction. It is also made sturdy enough to operate the starter drive lever many times over.

Plunger problems cause bad starter solenoid symptoms such the motor remaining active even after releasing the ignition key. That often results from corrosion or a return spring that has lost elasticity. Extremely cold conditions can also lead to a starter solenoid sticking.

4. Starter Solenoid Return Spring

Just as its name implies, the return spring pulls the plunger back after the end of solenoid operation. That happens when you release the starter key and the hold-in coil de-energizes or loses magnetism.

The spring must be a high quality material to perform this function or the plunger will not work correctly, especially over time. Malfunction happens if the spring loses its. tensional properties and cannot pull the plunger back. That usually appears as a starter solenoid stuck in the active state.

5. Starter Solenoid Contact Plate

At one end of the solenoid assembly sits a round plate. This part provides the surface to complete the starter motor circuit. When the plunger moves inside the solenoid toward the disc, parts make contact with the plate. The contact plate is made from a highly conductive material (usually copper) so that it offers the least resistance to current flow.

Over time, its surface can become pitted from the constant electrical connections. This reduces its effectiveness to complete the starter motor circuit and the solenoid loses efficiency. Car owners often turn the plate when that happens. This allows them to use the good surface and restore the solenoid’s operation.

Starter Solenoid Wiring

One of the most important topics when talking about starter solenoid is its wiring. This refers to the electrical circuit that makes the device operational (and which dictates the working of the whole starting system).

Starter Wiring Diagram

To help with explaining the electrical pathways, here is a starter solenoid schematic circuit showing the various connections. The plan represents as starter circuit that uses a combination of starter solenoid and starter relay.

starter wiring diagram

How to Wire a Starter Solenoid

From the starter solenoid wiring diagram, we see the various leads and circuits. These must be correctly positioned or the device will not work.

The cables leading to the starter solenoid connects to three terminals, B+S, and M terminals. The B+ terminal is the battery positive. It’s usually thick to withstand the large current needed to start the motor spinning.

The S connection receives the ignition switch current directly, connecting to the circuit either directly or by the action of a starter relay. The terminal links to the two solenoid wire windings, the pull and hold-in coils.

The connector leads to the starter motor. During the starter solenoid operation, the contact disc connects and B+ connections, thereby supplying current to the motor. At the same time, the action also disconnects the pull in coil.

Starter Solenoid Vs. Starter Relay

The starter solenoid is often called starter relay. While the names can substitute for either part, experts usually use them separately. The main reason is to differentiate between the two components and avoid confusion.

Starter solenoid is used for the device that acts as a heavy-duty switch for the high current circuit of the starter motor. Starter relay then refers to the small device that activates the starter solenoid. Technically, there exists fundamental differences starter solenoids and starter relays.

Starting with the starter relay location, the component is usually found away from the starter motor, acting as a remote switch for the stater solenoids. In contrast, the starter solenoid often directly attaches to the motor, although some do not.

As we have seen, starter relay function differs from that of the starter solenoid. The relay is a small switch that operates a low-power circuit. It only carries a few amperes in its circuit at any time.

starter solenoid starter relay

On the other hand, the starter solenoid is a high-current component. It mainly serves to switch on the starter motor circuit that carries many ams.The remote starter relay also only acts as a switch, whereas the solenoid serves two functions: switching the starter motor circuit and actuating a lever to push the starter gear.

In terms of construction, the starter relay consists of a single coil, while the starter solenoid contains two different coils; one to move the plunger and another to hold it. The starter solenoid connections and coils are also thicker, seeing that they carry large amounts of current.

what is a starter solenoid

Starter Solenoid FAQs

A starter solenoid is one of the most common automotive parts today. Surprisingly, a good number of car owners do not know much about it. We rounded up questions that people often ask about the component.

Q1. Are all solenoids activated by remote starter relay switches?

A. No, some automobiles use a starter solenoid that connects directly to the ignition switch a relay. It all depends on the preferences of the particular auto maker.

Q2. Is a starter solenoid a relay?

A. It is, however, it is usually called a starter solenoid or starter solenoid switch. This is to distinguish the device from the conventional starter relay, whose construction, function, and location are different. Both operate almost identically, though.

Q3. Is DIY starter solenoid repair possible?

A. You can easily fix common starter solenoid issues. It depends on the type and extent of damage. Some problems only require a little knowledge about the device. Others need you to take the car to a vehicle expert. In some cases, replacing the device provides the only solution.

Q4. What causes bad starter solenoid symptoms?

A. Many things cause signs of damage in a starter solenoid. Most of the time, it is bad connections, worn parts, or melted fuses and contacts. The return spring could also have lost elasticity, or the coil burned out. If the solenoid has been starting the motor for a long time, it is only probable that it will show signs of damage.

Q5. How long does a starter solenoid last?

A. The device usually almost lasts the lifetime of a car. The lifespan of most solenoids ranges from 7 to 9 years, although that also depends on the quality. You can also extend the usual lifespan using a starter solenoid rebuild kit to replace worn parts.

Q6. Can you just replace the solenoid?

A. You can, especially if the motor is in good condition and your budget does not allow you to change both. However, it is logical also to replace the motor. Doing so helps you avoid visiting the repair shop twice, which is most likely to be soon.

Q7. What is the starter solenoid price?

A. It varies and depends on the brand, application, quality, and other factors. However, the average cost ranges from $20 to $500. Aftermarket solenoids are cheaper when compared to the OEM options. Often when buying a starter solenoid, a little research of the market can mean a cost-effective purchase.

Q8. What is the starter solenoid replacement cost?

A. The cost to replace a starter solenoid can be between $120 and $ 600. It depends on the vehicle type and labor rates in your area. The amount also varies depending on the starter solenoid installation charges of the specific mechanic or repair shop.


The automotive starter solenoid is a small part of the starting system, yet one of the most indispensable. It serves two functions of switching on the motor current and acting as the starter lever actuator. You can feel its usefulness when you turn the ignition key, or when the car fails to start. We hope this guide provided you with valuable information about the device. We also believe it answered your starter solenoid questions.

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