Where Do The Wires Go On A Starter Solenoid?

If you’re having trouble figuring out which wires go where on a starter solenoid, you’re not alone. Many people struggle with this task, especially if they don’t have a lot of experience working on cars.

The good news is that with a little bit of guidance, you can easily figure out which wires go where and get your car up and running again in no time. In this article, we’ll take a closer look at the starter solenoid and show you exactly where the wires should be connected.

So, where do the wires go on a starter solenoid? To wire a starter solenoid, also called starter relay, correctly, the thick wire from the positive terminal of the battery should go to one of the large terminals on the starter solenoid, the other large terminal on the starter solenoid should have a wire that goes to the ‘S’ terminal on the starter, while the thin wire that comes from the ignition switch should end at the smaller post on the starter solenoid. Now, after starter solenoid, a starter comes that has its own solenoid and motor. The solenoid has one large terminal, which is for the battery and two small terminals. One smaller terminal of a starter solenoid (S terminal) is connected to the large starter relay terminal and the other smaller terminal connects starter solenoid with the starter motor. Typically, a starter does not have a separate ground terminal/wire. The casing of a starter is bolted to the engine, which is the ground “itself”. It is important to ensure that the wires are connected correctly, as incorrect wiring can cause damage to the starter motor or other components in the starting system. Lastly, keep in mind that some people also call a starter relay a starter solenoid. But, in literature, the starter solenoid is the component that is fixed to the starter motor. I will discuss more about this later in this guide.

Bonus Read: Where to hit starter with hammer

What Is Starter and Its Components?

The starter is a crucial component of the engine that is responsible for starting the engine of a vehicle. It draws electrical power from the battery and converts it into mechanical energy, which is used to turn the engine’s crankshaft and start the combustion process. 

The starter is located near the bottom of the engine. It is designed to crank the engine by turning the flywheel, which in turn initiates the combustion process. 

A starter consists of the following main parts:

  • Armature
  • Commutator
  • Brushes
  • Solenoid
  • Pinion gear

The internal view of a starter is shown in the illustration below:

internal view of starter


  1. Location of pinion shaft
  2. Flange
  3. Rolling element of freewheel clutch
  4. Mounting flange
  5. Solenoid coil
  6. Plunger
  7. Solenoid
  8. Contact bridge
  9. Battery connection
  10. Commutator
  11. Carbon brush
  12. Armature
  13. Pole winding
  14. Reduction gear
  15. Engaging fork
  16. Helix
  17. Meshing spring
  18. Freewheel clutch
  19. Pinion
  20. Stop ring


The armature, also called motor in a layman language, is the central component of the starter. It is a cylindrical core made of iron or steel that is surrounded by copper wire coils. When electricity from the battery flows through the armature, it creates a magnetic field that interacts with the field created by the permanent magnets in the starter. This interaction causes the armature to rotate.


The commutator is a component found on the armature. It is made up of a series of copper segments that are separated by insulation. The commutator’s primary function is to ensure that the current flowing through the armature’s coils always flows in the same direction. This is essential for ensuring that the armature rotates smoothly and efficiently.


The brushes are small carbon blocks that are mounted on the starter’s housing. They are in contact with the commutator and are responsible for transferring electrical current to the armature’s coils. The brushes need to be replaced periodically since they wear down over time due to the friction caused by their contact with the commutator.


The solenoid is an electromagnetic switch that is responsible for engaging the starter’s gear with the flywheel. When the ignition switch is turned on, it sends an electrical signal to the solenoid, which then pulls in a plunger. The plunger engages the starter gear with the flywheel, and the starter motor begins to turn.

Pinion Gear

The starter drive is a small gear that’s located on the starter motor. It’s responsible for engaging with the engine’s flywheel and turning it over. If your starter drive is damaged or worn out, you may have trouble starting your car.

What Are Terminals On The Starter?

starter terminals

Here are the common terminals you’ll typically see on the starter:

Terminal 1 – Battery Terminal

The first terminal you’ll see on the starter is the battery terminal. It is also called B terminal. This terminal connects the starter to the battery, providing the power necessary to turn the engine over. The battery terminal is typically the largest terminal on the starter, and is connected to a thick cable from the battery positive terminal. It’s usually located on the bottom.

Terminal 2 – Solenoid Terminal

The solenoid terminal is the smallest terminal on the starter, and it is responsible for controlling the starter solenoid. It is also called S terminal. The solenoid terminal is connected to the ignition switch, and when the key is turned, it sends an electrical signal to the solenoid, which then engages the starter motor.

Terminal 3 – Motor Terminal

It is also called the M terminal. This terminal connects to the starter motor via a small cable. When you turn the key in the ignition, the solenoid receives a signal from the ignition switch and sends a current to the starter motor through this terminal, which engages the starter with the flywheel and turns over the engine.

Terminal 4 – Ground Terminal

The fourth and final terminal on the starter is the ground terminal. It is not found on all starters as in most vehicles, the starter is grounded by bolting its casing with the engine. Starters, having 4 terminals, usually have a separate ground terminal as the 4th terminal.

This terminal connects the starter to the vehicle’s ground system, which is what allows the starter to complete the electrical circuit necessary to start the engine. The ground terminal is typically the smallest terminal on the starter, and it’s usually located on the top.

TerminalNameCable SizeCable ColorExplanation
1BatteryThickRedConnects the starter to the battery’s positive terminal.
2SolenoidSmallRed (may vary, depending on make and model)Controls the starter solenoid and receives signal from the ignition switch.
3MotorSmallBlue, white, or blackConnects the starter motor to the solenoid and turns over the engine.
4GroundSmallBlackConnects the starter to the vehicle’s ground system to complete the electrical circuit necessary to start the engine. Not found on all starters.

3 Pole Starter Wiring Diagram

3 Pole Starter Wiring Diagram

Note: In the above picture, you can see that I have shown all wires except the ground wire in red color. The red color represents hot. So, the thick cable from the battery will always be red in color.

In this diagram, the battery is connected to the solenoid via a positive cable. The solenoid has three terminals: the battery terminal, the starter terminal, and the ignition switch terminal.

The control circuit is connected to the ignition switch terminal of the solenoid. When the ignition key is turned, the control circuit sends a signal to the solenoid, which activates the coil.

The coil of the solenoid pulls the contacts together, connecting the battery to the starter motor. This causes the starter motor to turn over the engine and start the vehicle.

how current flows from battery to the starter motor when ignition switch is on

3 Pole Starter Solenoid Wiring Diagram

3 Pole Starter Solenoid Wiring Diagram

The starter relay, also called starter solenoid, works by completing and breaking the electrical circuit that supplies power to the starter.

The main reason a starter relay is used is to reduce the amount of current that flows through the ignition switch. When a vehicle’s engine is started, a large amount of current is needed to turn the starter motor.

If this current were to flow through the ignition switch, it could cause damage to the switch and lead to failure over time. By using a starter relay, the high current flow is redirected, and the ignition switch is protected from damage.

Here’s how a starter relay works, step-by-step:

  1. A small amount of electrical current from the ignition switch is applied to the relay’s coil, which is typically located between two input terminals on the relay.
  2. The electric current causes the coil to create an electromagnetic field.
  3. The magnetic field attracts a small metal switch (contact) located inside the relay.
  4. The movement of the switch connects or disconnects larger electrical circuits (called “poles”) located on the opposite side of the relay. Through these terminals, the current flows from the battery to the starter solenoid ‘S’ terminal.

4 Pole Starter Solenoid Wiring Diagram Chevy

In 4 pole starter solenoid, the mounting base is insulated, due to which there is a separate terminal for the ground connection. On the other hand, the 3-post starter requires a good bright mounting surface to ground. 

In a 4 pole starter solenoid, the ground connection is achieved by attaching a grounding wire to one of the starter terminals, which then connects to the chassis.

Some people also call a starter relay a starter solenoid. But, in literature, the starter solenoid is the component that is fixed to the starter motor. I will discuss more about this later in this guide.

The starter solenoid (the one attached to the starter motor) can be assumed as a larger relay to supply current to the starter motor.

On the other hand, a starter relay is used to supply current from the ignition switch to the starter solenoid.

Like a starter, a starter solenoid (also called starter relay as I said above) can also have 4 terminals in addition to a ground terminal. That fourth terminal is labeled as ‘I’ or ‘R’ terminal.

Difference Between starter and starter solenoid

In the picture above, one big terminal of the starter relay is connected to the positive terminal of the battery, and the other big post of the relay is connected to the S terminal of the starter.

Of the two small terminals on a relay, one is connected to the ignition switch and the other is considered as ‘I’ or ‘R’ terminal. That terminal delivers a full 12 volts to the ignition coil for a hotter spark when starting.

You can watch following video to get an idea how starter relay is connected toi the starter:

How To Test Starter If Car Is Not Starting?

To test the functionality of the starter in your car, you must first locate and remove it from its position. Depending on the make and model of your vehicle, the starter can be situated in different areas. For some cars, the starter might be situated beneath the engine, while for others, it can be found close to the engine block, which can be accessed by opening the vehicle hood.

Once you have removed the starter, two functional components determine whether the starter is functioning correctly. First, the solenoid, when operational, will lead to the disengagement of the starter motor gear from its casing, allowing the gear to come in contact with the flywheel. Second, the starter motor rotates on its gear, which, if functional, will encourage the rotation of the flywheel as well, commencing the engine’s ignition process.

You can watch the following video to test a starter:

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