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HomeTips & GuidesHow To Wire Starter Solenoid: Cable or Component Replacement

How To Wire Starter Solenoid: Cable or Component Replacement

A car’s starter motor consists of a motor and solenoid, and we’ll look at how to wire the starter solenoid in this article. 

The motor part of the starter assembly is responsible for cranking the engine to initiate its combustion cycle. 

If it does not work, it could be an issue with its solenoid, a component usually located immediately outside its housing. 

So let’s look at how to troubleshoot solenoid issues and wire it to solve your vehicle’s inability to start.

Table of Contents

What Is a Starter Solenoid?

A starter solenoid operates like a relay because it is an electromagnetically actuated switch. But instead of moving an armature to open and close the circuit, it has a captive metal plunger. 

When its coil gets energized, it moves this plunger from the neutral position to close the circuit and power the motor.

A starter solenoid

A starter solenoid

This component is essential in the starting system because the starter motor has a high electrical current draw.

The electromagnetic switch separates the high current circuit from the ignition switch, making it safer to switch on the engine using the ignition key.

Starter Solenoid Types

Starter solenoids can have three or four poles, where poles refer to terminals.

Three-Pole Solenoids

3-pole solenoids are the most typical type, and the terminals have these functions.

  • Battery/input terminal: connects to the battery’s positive terminal
  • Start terminal: links to the ignition switch via the ignition wire
  • Motor terminal: supplies power to the motor when the electromagnetic windings get energized and close the circuit

These solenoids don’t have a separate ground terminal because grounding occurs through the solenoid’s case or frame. So when you bolt the entire starter motor assembly to the engine, it has sufficient grounding.

A 3-pole solenoid attached to a starter motor (motor terminal already connected)

A 3-pole solenoid attached to a starter motor (motor terminal already connected)

Four-Pole Solenoids

This device is similar to the 3-pole starter solenoid but has an additional thin metal stud terminal that resembles the start terminal. The 4th terminal connects to the ignition coil or ballast resistor but usually remains unused.

This solenoid can have a separate ground wire terminal or use the engine ground like the 3-pole type.

A starter solenoid

A starter solenoid

In both solenoids, the battery and motor poles are thicker terminals than the ignition switch terminal because they handle high electrical current levels.

How a Car Starting System Works

The starter motor converts electrical energy from the battery to mechanical energy to crank the engine. This process begins in the ignition switch circuit.

When you turn on the key switch, you close the circuit that sends the ignition switch power supply to the fuse, then the safety switch.

A driver turning on the ignition switch

A driver turns on the ignition switch.

This safety switch triggers the starter-mounted solenoid, energizing its electromagnet to move the plunger and connect the starter motor to the battery’s power.

The motor pinion gear then turns the engine flywheel to crank and start it.

Once the engine starts, a one-way clutch separates the motor’s armature from the flywheel to prevent burnout caused by overspeeding.

How To Troubleshoot Starter Solenoid Issues

Before you get to wiring the starter solenoid, it is vital to confirm the location of the starting problem. It can be the starter solenoid wiring, battery, motor, or solenoid.

So begin by checking the battery’s voltage using a multimeter across the battery terminals. If okay, check the solenoid, a tiny cylinder mounted on the starter motor housing.

Have someone turn on the ignition switch and listen for a clicking sound from this component. When the solenoid engages successfully, it produces a clicking sound (coming from the plunger making contact).

A dismantled starter solenoid

A dismantled starter solenoid

So if you don’t hear the clicking sound, the solenoid wiring might be faulty.

And remember, the solenoid has a control circuit terminal for the ignition switch and an input terminal that connects to the battery’s positive terminal.

The issue can be in either of the wires connecting to these terminals. Or it could be a faulty starter solenoid.

But the output wire or motor might be faulty if the solenoid clicks and there is no cranking.

However, successive clicking sounds with grinding noises are not a good sign.

These symptoms indicate a defective solenoid that needs a replacement.

If you are conversant with starter motor assemblies, you can listen to the clicking sound for further analysis.

A weak clicking sound implies a faulty solenoid or ignition switch circuit.

Troubleshooting Solenoid Weak Clicking Sounds

You need to test the solenoid current and voltage drop to pinpoint the cause of the problem.

Solenoid Electric Current Testing

Current testing checks the thin ignition wire that completes the control circuit to energize and activate the solenoid.

You can use a jumper wire to bypass the ignition switch by connecting the input terminal to the start terminal. You should hear a clicking sound.

If the sound is still weak, the issue is in the solenoid, not the wiring. But if it sounds louder, the problem is along the ignition wiring.

And if there is no clicking sound, check if the battery’s electric current reaches the solenoid’s input terminal. You can use a test light, tester, or multimeter.

Solenoid Voltage Drop Testing

A weak clicking sound can also be due to an insufficient power draw from the battery due to increased resistance along the input terminal power supply line.

Use a multimeter for this test and set it to 20V DC. First, measure the voltage across the battery terminals, which should be around 12V.

Have someone turn the ignition switch while observing this voltage reading. You should notice a slight voltage drop (around 0.5V) caused by the starter motor power draw.

A technician using a multimeter to test a car battery

A technician using a multimeter to test a car battery

Next, connect the multimeter positive probe to the solenoid’s output/motor terminal and the negative probe to the input terminal.

Have someone turn on the ignition switch and observe the voltage drop. This value should match the one on the battery.

If the values match, the issue might be the wire connecting to the starter motor or the motor itself.

But if the voltage drop is too high, the input power line is faulty (high resistance). And if less than 0.5V, the solenoid might need a replacement.

How To Wire Starter Solenoids

You must replace the damaged component (solenoid or motor) or the wiring once you’ve identified the problem source. If replacing the solenoid, ensure you get the terminal connections correct.

Generally, the starter solenoid wiring diagram is standard in most vehicles and will guide you when replacing the wires or components. And always begin by disconnecting the positive wire from the battery.

A car starter motor/solenoid wiring diagram

A car starter motor/solenoid wiring diagram

Wire replacement is easy because you only have to install new wires or splice new pieces to replace the damaged sections by crimping them.

But replacing solenoids is more complex. They can be starter-motor or remote-mounted, but the former is more common.

And the motor is usually low down near the engine’s rear section. So follow these steps to access and replace it.

Wiring Steps

  1. Park the car on a solid surface, then disconnect the battery. Lift the car using a jack, place your jack stands under the vehicle, and go under to locate the starter assembly.
A car placed on a jack stand

A car placed on a jack stand

  1. Note the wire color coding or mark the starter solenoid wires to remember the connections. Most have three terminals, so note the three wires.
  2. Disconnect the solenoid’s wiring using a wrench, then remove the mounting bolts that attach it to the motor housing.
  3. If you can’t access the solenoid without removing the entire starter motor assembly, unscrew the unit, then unbolt the solenoid when out of the vehicle.
  4. Separate the solenoid from the motor, then attach the new one. Ensure the old and new units have the same number of terminals.
  5. Bolt or screw the new solenoid to the motor casing. If you had to remove the motor, install it back into the vehicle.
  6. Reconnect the wires correctly and tighten them in the respective terminals.
  7. Connect the positive cable to the battery, then try to start the car.
  8. If the engine roars to life, turn it off, then lower the vehicle to the ground.

Wrap Up

Replacing and wiring a starter solenoid is not a challenging task, but you need to identify the source of the problem first. So we’ve explained the troubleshooting steps above in detail. 

So if the issue is along the wires, follow them from source to destination to find the damaged area or replace the cable. But if the solenoid is faulty, use the steps above to wire its replacement. 

That’s it for this article. Comment below to let us know if you managed a successful solenoid wiring.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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