How to wire up a Starter Solenoid: An Ultimate Guide on Starter Solenoid Wiring


A starter is essential for cranking the vehicle in the engine. It has two main components, the motor and the starter solenoid. To move the motor, you need to control the starter solenoid. This article will teach you how to wire up a starter solenoid

Table of Contents

What is Starter Solenoid?

Two components make up the entire starter motor and solenoid combo. The Solenoid is the smaller of the two cylindrical parts, while the motor is more significant. Essentially, a starter solenoid is just an electromagnetic switch.

It essentially has two extensive contacts to link the input/output terminals.

Moreover, a magnetic coil within that physically connects and separates the contacts.

These contacts can handle high currents while the magnetic lock operates at low voltage and current.

Why is the starter Solenoid necessary?

Besides a few hybrids, nearly every car on the road today has an internal combustion engine.

To get it going, you need a starter motor. However, it’s usual to employ a direct-drive or a gear-reduction starter in a car. The two designs share the same functional principles.


  • The Solenoid interacts with a plunger, which then manipulates a lever fork within the starter when the key turns to the “start” position.
  • The fork brings the starter’s pinion gear into mesh with the engine’s flywheel or flexplate.
  • The solenoid plunger also presses a disc into contact with the device’s terminals. After making contact, electricity can flow from the battery to the starter.
  • To reach the field coils and armature windings, the current must first go through the insulated brushes of the starter, which ride on the commutator.
  • The current passing produces a magnetic field through the field coils and armature, which in turn causes the armature to spin.
  • The commutator keeps the armature rotating in the same direction by constantly switching the circuit’s polarity.
  • When the armature of a direct-drive starter spins, it immediately rotates the pinion gear. In contrast, if the starter uses a gear drive, the armature rotates a series of kits, which turns the pinion gear.
  • The flywheel is rotated by the starter’s pinion gear whenever the engine is turned on. The pistons, camshaft, and other moving parts are activated in an internal combustion engine because the flywheel is attached to the crankshaft.

The engine starts when air, gasoline, and a spark are introduced. You can turn off the starter motor to the “run” position by turning the ignition key.

In this method, the starter is protected from the force exerted by the rotating engine. The starter includes a one-way clutch that allows it to freewheel if the driver doesn’t engage it.

Caption: Diagram showing a car starter system

Types of Starter Solenoid

Some enthusiasts who want to connect the solenoids don’t know about the wiring scheme. Also, you might think that all wirings are the same. However, it depends on the type of starter solenoid you have.

Three-pole or three-terminal starter solenoid

A typical starter solenoid has three connections at its terminals:

  • One terminal is the “B” or battery terminal, which connects the Solenoid through the positive battery cable.
  • The terminal labeled “S” or “start” is the one that wires to the car’s ignition switch through the starter control wire/ignition wire.
  • The “M” or “motor” terminal is the one used to connect the starter motor’s cord.

Starting occurs as the driver moves the ignition key to the “start” position, which causes power to flow to the starter’s “S” terminal. Moreover, this voltage powers the magnetic coils in the Solenoid.

The magnetic field generated by the windings pulls the starter’s plunger, which presses a plate against a set of links.

These contacts have to go onto the “B” and “M” terminals of the Solenoid. When the terminals are connected, power can flow from the power supply to the starter motor, allowing the latter to turn the engine over.

Caption: starter-mounted Solenoid with three terminals


4-pole starter solenoid

The hot wire from the power supply is connected to one of the larger terminals, whereas the starter connects to another terminal.

The ignition switch links to one of two smaller nodes, and the second relates to the ignition coil or blast resistor. Be cautious about setting the frame on solid ground. It may also be left as it is.

4-pole starter solenoid

Caption: 4-pole starter solenoid


How to Tell If a Starter Solenoid Is Bad?

You can test the car ignition system using two tests.

Preliminary Testing

  • Set the parking brake to on and the transmission to “neutral.” It is critical for safety reasons.
  • Check if the system does not have a dead battery. If it has, you need to solve these problems first.
  • Now, check the wiring to the Solenoid, as the wires can have corrosion and loosen up.
  • Detach the wires that are going around the Solenoid and start the car. If the Solenoid doesn’t click, it is problematic, and you need to replace it.

Solenoid Bench Test

Remove the starter motor and the Solenoid from the car to perform the bench test.

  • Fix the starter motor properly so that it doesn’t move when activated.
  • Provide 12 volts to the input terminal of the Solenoid and attach the negative wire to the car metal frame.
  • If the solenoid clicks and the starter motor turns on, it’s perfect. However, if it doesn’t, you need to replace the Solenoid. Use the jumper wire to link the small and big terminals of the Solenoid.

How to Rewire a Starter Solenoid and Starter Solenoid Wiring Diagram

As the starter is installed on the engine, the Solenoid is often wired in simultaneously. Remotely placed solenoids are commonplace on Ford vehicles. Manufacturers set the solenoids conveniently in the engine near the battery, streamlining the hiring process. Whether your Solenoid is an on-starter or a remote-type, you can wire it in a moment with our help.

Main parts of Starter Solenoid

There are three components of starter solenoid wiring.

  • Fuse
  • Ignition Switch
  • Starter Relay
an easy wiring and a complete wiring

Caption: an easy wiring and a complete wiring


On-Starter/ Starter-mounted Solenoid Wiring

  • Disconnect the negative wire (black) from the power source.
  • Elevate the car using a jack while supporting it on a stand. It might be possible that you have to install the wire under the car.
  • Take the starter to the mounting bracket and make the electric connections. It is because the starter solenoid is heavy to hold in one hand.
  • Use a socket, wrench, or ratchet to connect the red wire on the ignition terminal and the Solenoid. also, if there is space, thread the starter mounting bolts to it.
  • Ensure you have connected the wires properly and finish mounting the starter on the engine. Reconnect the black negative cable.

Remote-Mounted Solenoid Wiring

  • For remote-mounted solenoid wiring;
  • Disconnect the black cable from the power source
  • Fix the Solenoid in the engine compartment with the help of a socket and a wrench.
  • Connect the red cable of the battery with a large bolt on the left of the Solenoid.
  • Link the starter cable to the large bolt on the right of the Solenoid and the control wire to the control circuitry.
  • Attach the other small cable to the ignition bypass terminal on the right of the Solenoid and reconnect the black negative wire. 
Starter Solenoid Wiring Diagram

Caption: Starter Solenoid Wiring Diagram


Starter Wiring Mistakes You Need To Avoid

If it is faulty, your whole system is unable to work. So, it would help if you wired it so the issues do not occur while starting a vehicle correctly.

Common Weaknesses On The Activation Side

The primary wire is usually more extensive, while the activation wire is generally smaller in high-performance starters. The starting switch connects to the activation wire, which signals the ignition system.

In races, problems might arise when the activation wire is too short, as the Solenoid’s coil will not provide enough “pull” to propel the vehicle. However, your power system’s switch and the solenoids will deteriorate over time.

To top it all off, ensure the electrical rating of any controls in that circuit is higher than the power requirements of your starter.

If you don’t wire a starter according to specifications, it will cause problems for the entire electrical system. Also, if you do not wire the starter correctly, the voltage it generates can quickly burn out switches and other sensitive devices.

Common Weaknesses On The Main Wire

The power to spin the wheels of the industry comes from your primary starter wire, so it must be of the highest quality.

Despite the belief of many competitors, the wire they are employing may not provide the necessary current to keep a starter happy.

The size of the positive wire is essential, but so is how the starter is grounded. A dedicated ground is recommended for one of several methods to earth the starter.

Now, you may verify the health of your primary wire with various methods. The simplest way is to double-check every connection you make.

Hence, examine the crimps to ensure they fully engage in the system and check that the entire wire touches the solder and connector whenever possible.

Moreover, corrosion is your adversary; you must remove all evidence. Also, check to see that there are sufficient relays in operation. False relays will weaken and collapse over time.


Solenoids are used to activate and control high-current circuits with much less energy than the current the Solenoid will be responsible for.

Moreover, in a solenoid, a coil creates an electromagnetic field that pushes a plunger, which forces the higher electrical switch to the closed state when a tiny current is provided to the Solenoid. 

Nothing beats the convenience and security of solenoids when it comes to turning on and off electrical devices. At Cloom, we offer wiring harnesses to make your electrical connections reliable and safe.