How to Wire a Starter Solenoid: Automobile Guides

Are your mechanic bills spiraling out of control?

Chances are you are paying for a repair job you could do yourself.

Unfortunately, many modern vehicle owners lack the basic knowledge of how a car functions.

For example, do you know where your car’s starter solenoid is?

Or Are you aware of how to wire a starter solenoid?

If the above questions sound Martian, buckle up and continue reading.

Below is Cloom’s DIY guide on the starting system.

With this information in mind, you can replace the starter solenoid or relay it yourself.

What is A Starting System?

Diagram showing a car starter system

Diagram showing a car starter system

Although technology has changed much of what is in a car, the ignition components are still more or less the same.

Battery Cables

Car battery cables

Car battery cables

For your engine to start, it needs a high current which usually comes from your car’s battery.

The cables that carry this charge from the battery must be thick enough to withstand the high amount of electricity flowing through them.

When you look at your car battery, you usually see two cables.

These cables connect the battery to your car’s starting system.

First, the red one connects the starter solenoid to its positive terminal.

This wire is usually live, so be careful when handling it.

Then, a black or greenish-yellow cable connects the starter motor to the battery’s negative terminal.

Starter Relay

Car starter relay

Car starter relay

A starter relay controls when the high current flows to the starter motor.

That is, it’s responsible for igniting the starter solenoid so your car can start.

It does so by sending current to the ignition switch.

As such, you can use the battery power for other things, such as using your power windows and car radio without cranking the engine.

The starter relay is thus crucial to the ignition because the high current passing through would fry your car if the relay weren’t there to keep it safe.

Starter Motor

Assorted Car Starter motors

Assorted Car Starter motors

The starter motor is the reason why your car’s engine starts.

It’s usually around where your car’s engine is, but it could also be a separate unit like in BullDozers.

It needs a healthy supply of 12-Volt charge from the battery to perform.

Neutral Safety Switch

neutral safety switch

neutral safety switch

A neutral safety switch prevents your car from jerking when the engine starts.

The neutral safety switch usually works the same in automatic and manual cars, using your car’s PCM inputs to engage.  

Starter solenoid

starter solenoid

starter solenoid

The starter solenoid has two functions in your car’s starting system.

Firstly, it completes the circuit between the starter motor and the power source (car battery).

Then, it engages the starter gear to the engine flywheel facilitating it to crank up.

How does the starting system work?

Start the engine

Start the engine

Moving the ignition to start allows the current to flow to your starter solenoid.

Next, the starter solenoid pushes the motor gear to engage with your engine’s flywheel.

So, the starter motor turns the flywheel that spins the crankshaft, forcing the engine to start.

You should also know that the starting system only works when the car is in Neutral or Park.

Furthermore, the system cuts off once the engine starts revving.

Symptoms that you need a replacement of your starting system

Do you know that most problems are related to the solenoid?

car starting problems

car starting problems

You are missing the distinct click noise when starting the engine.

Most cars produce a clicking sound right before an engine starts.

It results from the starter relay switch completing the circuit and the starter solenoid engaging the starter motor with your engine’s flywheel.

So, failure to hear this sound when powering your car indicates a problem with one of the two.

You experience a continuous clicking noise when starting your engine.

Any rapid noises from your vehicle or show that something is wrong.

For example, if your car keeps clicking rapidly with each start, you have solenoid problems.

In most cases, such noises mean the power received is not enough to start your motor.

So, before you rush to replace your solenoid, check your battery and alternator first.

Your engine has a noticeably slow crank.

Engine cranking is a fast motion that only takes a few seconds.

Yet, sometimes your car sounds like it is struggling to get going.

Some instances may result from a low battery.

But, if the issue persists after jumping the power source, the chances are that you have a solenoid with burnt contacts.

Thus, your only way out is to replace it with a new one.

No crank of the engine.

Finally, you know you must replace your solenoid when your engine doesn’t start.

For example, as you turn the ignition key, all car functions are fine, but the starter motor won’t engage no matter what you do.

The first opinion is to check for poor connections.

If everything is fine, then your best bet is to replace the starter solenoid, which is likely why your car won’t start.

Then, How do you Wire a Starter Solenoid?

Starter solenoids come in two types.

Firstly, you can use the on-starter solenoid that directly mounts on your car’s starter motor. 

Or, you can also opt for a remote-mounted solenoid.

These types of solenoids operate across a wide temperature range and are pilot-operated.

Additionally, they feature a single coil spring return and come with SIL 2 & 3 certification.

Furthermore, they can either feature a 3-pole or 4-pole solenoid switch.

The procedure is different when you use either pole.

On-Starter Solenoid vs. Remote-Mounted Solenoid

on-starter solenoid

on-starter solenoid

  1. First, secure your vehicle using chokes on the front and back tires. Then, disconnect your car’s negative battery terminal.
  2. Secondly, lift your car using the stock jar to a height with enough space to get underneath. Additionally, add a jack stand near the jacking point for extra security.
  3. Then, crawl underneath and mark each wire referencing their respective connection locations. You can use masking tape and a marker for the labeling. Additionally, use a wrench to disconnect each wire and unplug the wiring harness from the solenoid.
  4. Subsequently, remove the starter motor carefully by unbolting it from your engine. You will need to unbolt remote-mounted solenoids for their specific installation area.
  5. Finally, reconnect the wires to the new solenoid as per the labels. Then, lower your car from the jack and reconnect your battery’s negative terminal.

3-pole starter solenoid vs. 4-pole starter solenoid

4-pole starter solenoid

4-pole starter solenoid

The main difference between a 3-pole starter solenoid and a 4-point starter solenoid is how they work and their connection to the field coil.

In 4-pole starter solenoids, the four terminals speed up the motor.

On the other hand, in 3-pole solenoids, the terminals’ primary function is to launch the starter motor.

Furthermore, 3-pole solenoids feature a series connection with the field coil compared to the parallel one in 4-pole solenoids.

Thus, 4-pole solenoids can still function with varying battery charges since the NVC and field winding are on different circuits.

Below is how you can wire a four-pole solenoid.

  1. First, connect one of the large terminals directly to the hot wire from your car’s battery. Then, affix the other large terminal to your starter.
  2. Secondly, connect one of the small terminals to your starter switch, with the other connecting to either the ballast resistor or ignition coil.
  3. Finally, reconnect the car battery’s negative terminal to complete the installation.

Three-pole solenoids follow a similar procedure.

However, they do not have a smaller terminal for the ballast resistor or ignition coil connection.

How to Wire Starter Relay?

Cloom recommends using an AWG 4 gauge cable for this connection.

It can handle the high voltage electrical connection from your car battery.

Additionally, it is strong enough to withstand damage from any electrical fault should it occur.

Car starter relay

Car starter relay

  1. Initially, disconnect both terminals of your car battery. You do this as a safety measure to prevent accidental electrocution during installation.
  2. Then, remove the faulty starter relay by unbolting it from the engine bay and replacing it with your new relay.
  3. Next, identify the wire from your starter solenoid and connect it to one of the big terminals of your new relay. Additionally, you can join it to either of the big terminals as they can accommodate the high current from the battery.
  4. Locate the thin wires from your key switch and fasten them to either the small terminal of your starter wiring relay. If you only have one small terminal, mount the other wire to the relay’s casing or any part of your car’s engine compartment.
  5. Finally, connect the remaining big terminal to the wire from your car battery’s positive terminal. You can identify this by its red insulation color and its thickness. You can also use an appropriate gauge wire in the installation if the stock option is unavailable.


Starter solenoids and starter relays are essential parts of any vehicle’s ignition system.

They need regular maintenance checks and wiring to continue working properly.

But no matter what kind of help you need, Cloom is always available to provide you with the best automobile wire harness solutions and guides to ensure your vehicle is always running. 

Hey, I am John, General manager of Cloom and OurPCB.

I am a responsible, intelligent and experienced business professional with an extensive background in the electronics industry.

Reach me at [email protected] to get a quote for your projects.


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