Starter Relay: The Ultimate Guide
When starting a vehicle, different parts are involved. One of them is the starter relay, a small but crucial component of the starting system. Many people mistake the starter relay for the starter solenoid, thinking the two to mean the same thing. Some websites even contain information that says so. However, that is not true.
While both components form part of the starting system, they are very different. The starter relay switches on the current that activates the starter solenoid. The starter solenoid, on the other handed, closes the switch for the starter motor and usually mounts on the motor. It is usually bigger than the starter relay and of heavier construction.
This guide contains information about the automotive starter relay. In it, you will find all there is to know about the starter relay: what it is, its location in a vehicle, how it works, and its function. We also included information about the signs of a bad starter relay, how to test it, and how to replace or fix a bad one. Read on to learn more.
Table of Contents
Starter Relay Definition
What is a Starter Relay?
A starter relay is a small, electrical device found in the starting circuit of high-current motors. The relay is essentially a remote switch that controls a high-current circuit. In motor vehicles, a starter relay uses the small ignition switch current to close the much heavy-duty starter circuit.
In some automotive applications, the starter relay works together with the starter solenoid to operate the starting system. In others, the ignition switch operates the starter solenoid circuit directly. These are usually the small vehicles whose starter motors do not require large amounts of current to work.
Apart from cars and trucks, starter relays can be found in many other applications where electric motors are involved. These include motorcycles, refrigerators, lawnmowers, and more. A starter relay in fridges operates the compressor, ensuring the motor starts without damaging the switches. The starter relay in bikes works the starting circuit much similar to how a car starter functions.
Is the Starter Relay the Same as starter solenoid?
The starter relay is often confused with the starter solenoid. That could possibly arise from the fact that both act as relays. But contrary to what some people think, the two names do not mean the same vehicle part. One of them is only a switch while the other is both a switch and actuator. Here are the ways these two auto parts are different.
Starter Relay Vs. Starter Solenoid
A starter relay is a smaller size when compared to the heavy-duty starter solenoid. It essentially comprises a magnetic core with a wire wound around it. On one end of the core is an armature or plunger that closes contacts to work a switch. It is spring-loaded, a construction that helps to push it away from the contacts when the core loses magnetism.
A starter solenoid is usually bigger than the starter relay. The solenoid’s internal construction consists of two coils of wire and a magnetic core towards one end. The core is free to move in and out, with a return spring on one end. The other end is where current enters the solenoid and contains the various connectors.
Both the starter relay and starter solenoid operate almost identically. A current flows throw the coil winding and produces an electromagnetic field. In a starter relay, the magnetism moves an armature or plunger to close a circuit.
In a starter solenoid, the magnetic force created by current flowing through the coil causes the core to move out. The moving plunger does two things. It closes contacts that switch on the starter motor. It also moves the pinion gear to engage the flywheel.
As we can see, a starter relay only acts as a switch. The starter solenoid, on the other hand, both closes a circuit and moves a gear to act as an actuator. The starter relay is usually mounted a far distance from the starter motor, while most starter solenoids attach to the motor housing.
How Important is a Starter Relay to the Engine?
Here is how. For the engine to start, it has to receive torque from outside. In vehicles that use an electric starter, a motor provides that starting force. Now, the starter motor used in most vehicles is a power-hungry device. To start spinning, it can draw from a few to many amps depending on vehicle type and make. This is a very high current that requires thick cables to heavy-duty components in the starting circuit.
The ignition switch comprises delicate parts and very thin wires. If the amount of current required by the motor were to pass through it, a lot of damage would occur. The wires and other parts of the switch would melt from the resulting heat- even vaporize. The starter relay prevents this from happening by allowing the starter current to bypass the ignition switch.
Were it not for the relay, the ignition switch would need to be made of large parts and thick wires. This would not be practical due to the location of the component in a vehicle. It would also be expensive to make automobiles with big ignition switches and corresponding wire sizes. A relay eliminates these challenges and manufacturing costs.
What is the Starter Relay Function?
It allows a large current to flow when you turn the ignition key or press the start button on your car. The ignition switch cannot handle the large current required by the starter motor. Without the relay, it would burn out. As we have seen, doing away with the relay would mean a large ignition switch and thick wires, both impractical solutions in a typical automobile.
If the starter relay is not working, it can mean a vehicle that will not start. Reasons as to why this component would fail vary, as we will see later. They also require different solutions depending on the type and extent of the damage. There are those that can be repaired and others that need a new relay installed.
Where is the Starter Relay Located?
The starter relay location may vary depending on the vehicle type and model. It can be in the fuse box (also called a power box), the fuse panel under the dash, or on the right fender. Most cars will have it located under the hood, inside the long box with a black cover. Often called the fuse box, this is where a vehicle’s fuses and relays are mounted. The box is usually installed on the driver’s side.
Because the fuse box contains may different fuses and relays, it may be difficult to single out the starter relay. In that happens, we recommend that you use your car’s manual. It will have the identity of every component in the box. The manual will also help you find the relay if it’s location is not the one described here.
When mounted in the fuse box under the dashboard, a starter relay may not be easy to locate, or even comfortable to remove. Starter relays that attach on the fender wall may not be difficult to find. Usually the cylinder type, these relays can be recognized by their mounting posts and leads. If unsure, the vehicle manual can be used to confirm the location of the starter relay.
The starter relay is made up of different parts, some moving and others immovable. In the next part of this guide, we examine this starter system component in detail; how it looks like and its internal construction. That will help you to understand how it works better. You will then be able to tell when the relay is working and when faulty.
Starter Relay Diagram
Starter relays may look different across brands and vehicle types. However, they operate the same way and perform a similar function. Looking inside these components, you will realize that they have identical parts. A typical starter relay consists of housing, coil windings, magnetic core, and an armature or plunger. The internal construction forms an electromagnetic switch that a driver operates remotely when starting a vehicle.
How Does a Starter Relay Look Like?
Although starter relays use similar mechanisms to operate, they differ in the way the look. Fuse box starter relays are a box construction, with pins or connectors protruding from the housing. Behind the connectors are the internal components, which consist of an electromagnet, armature or plunger, and contacts. These relays often have more than two connections for the primary side.
Fender-mounted starter relays are mostly the cylinder types. They are a basic construction with only four connection points. You can recognize these relays by their two big posts and another pair of small ones. Unlike the fuse box types, fender-mounted starter relays only use two connectors for the primary or coil side. Here are pictures showing the two kinds of starter relays.
Inside a Starter Relay
The main parts of a typical starter relay include
Armature– this is the part that gets by the iron core when current passes through the coil windings. The armature is made from a magnetic material so that it is strongly pulled when the core becomes magnetized.
Spring– the spring tensions the armature, allowing it to return to the original position when the ignition switch is turned off. Without the spring, the relay might keep the contacts together, causing the starter to operate for longer than is necessary.
Coil windings– the coil receives current from the battery when the ignition is turned to the start position or when the start button is pressed. As a result, it creates a magnetic field to cause the iron core to become magnetized and move the armature or plunger.
Iron core– the iron core magnetizes when the coil would around it is energized. This causes it to push or pull the armature to close contacts. The closed contacts complete the circuit that should provide the starter solenoid with current from the battery. The core is made of iron to enable strong magnetization as well as lose it instantly when the ignition is turned off.
Contacts– these close the switch on the secondary circuit. This is the switch that operates the starter. The contacts should be made of highly conductive and hard-wearing material, among other properties. If there is corrosion on the surface, the relay cannot operate as it should. Also, if the contacts melt to weld together.
Other parts include the yoke to hold the electromagnet, insulators to prevent shorting, and the relay housing to protect the internal components and provide mounting surfaces.
The box-like starter relays found in many motor vehicles use the DIN 72552 standard numbering systems for the different terminals. These numbers are usually molded on the relay housing with a They are
85– for the coil terminal on the primary side of the relay
86– for the other coil terminal
87– used for the normally open (NO) contact terminal that switches the starter current on
87a– used to denote the normally closed contact terminal on some relays
30– the common connection for both 87 and 87a terminals
The 86 terminal receives the 12V input of the battery through the ignition switch. The 86 terminal is usually grounded through the vehicle body, allowing current to flow through the relay coil windings. However, the orientation or polarity does not matter as long as the relay does not use a diode.
The cylinder types of starter relays feature connection posts. The two small terminals are the coil connections with one marked “S” and the other “I”. These terminals connect to the ignition switch to supply current to the coil when the ignition key is turned to “start”. The other big posts are the starter circuit terminals. One connects to the battery and the other to the starter.
How Does a Starter Relay Work?
Different vehicles may use different starter relays. However, the working of the relays is usually more or less the same. They are essentially a mechanical switch that is worked by an electromagnet. Differences mainly occur in the number of connections, with some relays having more than two connectors on the primary side. Here is how a starter relay works.
When you turn the ignition key to the “start” position or press the start button, the ignition circuit closes. The “S” terminal ( or 85 terminal in some relays) receives a 12-volt signal from the car’s battery. A small current, usually less than 10 amperes, passes down the terminal and through the coil windings and through to ground. In the fender-mounted relays, this is the “I” terminal. In fuse box starter relays, the ground is terminal 86.
Current in the coil causes a magnetic field. The iron core becomes magnetized, causing the armature to move and close contacts. With the gap between the contacts of the starter circuit closed, the starter solenoid receives voltage from the battery and current flows through its coil windings.
When the engine has started, a reverse action is activated by the driver by turning off the ignition. The starter relay coil is deprived of current, causing it to lose magnetism. It no longer attracts the armature. Because the armature is tensioned by a spring, it will move to open the contacts it had closed.
The result is lack of electric power in the starter circuit. The solenoid coil loses magnetism, and the plunger returns to its position. The return causes the contacts that had closed the starter motor circuit to open, and the motor stops running. The relay is now ready to operate the starter circuit again.
Starter relays are built to last a long time. With only a few moving parts, it cannot be expected to fail easily or quickly. Despite that, these components to break down. A bad starter relay can cause you to become stranded when you cannot start a car. How can you know when the relay in your car is failing to take action? The next chapter shows you how.
Symptoms of a Bad Starter Relay
The starter relay is a small vehicle, and perhaps the reason why car owners often neglect it. Although the component only contains a few moving parts and lasts a long time, it can break down and cause starting problems. The relay switches a circuit that works the starter. If it fails, can mean an engine that does not start straight away, or one that does not start all.
Starter relay problems can have many different causes. Some can be corrected, while others cannot be fixed and require a replacement of the relay. Before looking at the causes of failing starter relay, about symptoms that should prompt you to take action.
How to Tell if a Starter Relay is Bad
A starter relay not working will give specific signs. As you will notice, all involve starting issues. They are:
- No Crank, No Start
The starting process fails completely. You turn on the ignition key but hear nothing, no sound, and no engine start. This symptom can show a starter relay is bad, but also a dead battery. To confirm the problem to be the relay, you would need to test the battery’s operation by switching on the car accessories. If in good condition, the suspect could be the starter relay.
The starter relay enables the flow of current to the starter solenoid and motor. If it fails completely, it means the starter solenoid not working the plunger, and the motor not coming to life. If this happens when the battery is working and the connections are in perfect condition, the relay needs replacing.
- Clicking Sounds
A clicking starter relay switch indicates a working coil but failing contacts. It occurs when the relay cannot conduct enough current for the secondary circuit. As it tries to close and open the contacts, you will hear a series of clicks. This problem often results from corroded or burned out contacts, which often happens when the relay is too old.
Because the relay is still operating, you can remedy the problem by cleaning the contacts. The battery would also need to be checked. That is because a weak battery one can cause the starter relay clicking problem, among other issues. The starter relay circuit, too, would need to be inspected for worn or damaged cables or connections.
- Irregular Starts
A vehicle is supposed to start at the first attempt. If that does not happen, the reason could be a failing starter relay. This symptom shows up as occasional starting fails, indicating dirty or greasy connections. It could also be a problem of excessive heat affecting the relay.
Cleaning the connections can restore the efficiency of the device. Repairing broken leads, too. However, that is only if other parts of the relay are not ruined. Otherwise, a replacement would be necessary. But we would recommend changing the relay, especially if you cannot pinpoint the exact problem.
- Starter Remaining On
Normally, the starter system should stop operating when the engine has started and the ignition switched off. If it stays on, it means the starting circuit is still closed. Because the starter relay switches the circuit on and off, a starter that stays on can mean a faulty relay.
This symptom often occurs when contacts have welded together. Even after you have switched off current to the relay to disengage the relay’s armature or plunger, nothing happens. The welded contacts stay together, keeping the starter motor on. Welded contacts often result from excessive current levels melting the metal surfaces, causing them to stick together.
Starter relay contacts welding together is a risky situation that requires immediate attention. That is because it can lead to damage of not only the relay but also other parts of the starting system. When starting a vehicle, always stay alert for a grinding noise when the car has already started and the ignition turned off. Replace a starter relay whose contacts have stuck together.
Causes of Starter Relay Failure
A starter relay goes bad for various reasons. They include the following
Dirt– although these components are usually protected by placing them under the hood or dashboard, grime, dirt, and debris can still reach them. Over time, the dirt builds up to a point where the relay cannot operate properly. When current cannot flow across the contacts efficiently, you may hear rapid clicks or buzzing sound coming from the relay.
Corroded contacts–corroded contacts or connections cannot pass current in adequate amounts. The result is a failing relay that causes starting problems. It can be erratic fails, unusual relay noise, or a vehicle that cannot start.
Bad leads– broken leads are another cause of a faulty starter relay. If enough current does not reach the relay, it cannot operate as required. It will show symptoms of failure, usually by producing sounds and struggling to operate the starting circuit. Apart from starter relay buzzing or clicking sound, the engine may fail to start.
Excessive heat– when too much current passes through the relay, it causes the contact to melt, leading them to stick together. The result is a relay that keeps the starter circuit closed even when the ignition is off. It is one of the starter relay problems that need immediate attention. Failure to act quickly can lead to starting system components getting damaged and costing you a lot to replace or fix.
Relay too old– starter relay failure does not need to have any identifiable cause. It can be simply that the relay has been operating for far too long. An old relay will have parts that are deteriorated to a point where they cannot work effectively. If that happens, nothing can possibly be fixed in most cases. Changing the component would be the only solution.
What options do you have to correct a bad starter relay? You can either choose to fix the problem or buy a new relay. The path to take depends on several factors. If the relay failure is caused by dirty contacts, cleaning them would cause current to flow again. Replacing worn or broken leads can also restore the operation of a failed starter relay. The other option is replacing the relay. Next, we look at how to fix starter relay problems.
How to Fix a Starter Relay
A bad starter relay can be repaired, especially if the fault involves dirt blocking the flow of current across contacts. Also, if the leads to the component are damaged. Before carrying out repairs, it is necessary to determine the kind of damage or fault. That is because some starter relay problems can be fixed while others require installing a new relay. To find out the issue with a starter relay and its circuit, a look at the tests to diagnose faults.
How to Test a Starter Relay
Things you will need
A 12-volt battery, digital multimeter (ensure it can read Ohms), alligator clips, and jumper wires. If you have a fender-mounted starter relay, you will also need wrenches and sockets.
Have the vehicle safely parked and the transmission in neutral or park. You do not want the vehicle moving forward accidentally when working under the hood.
Start by checking the battery condition. A weak or dead battery can cause symptoms similar to those of a bad starter relay, and you want to rule that out. To test the strength of the battery, switch on the vehicle accessories to see if it can power them.
For a more definite or accurate diagnosis, you may test the battery’s voltage. It should read not less than 12 volts (we are assuming the vehicle uses a 12V battery). Should you find your battery to be weak, it would be advisable that you get a better one and use it to test starting problems.
Locate the relay. It will be in different places depending on the particular vehicle. Some vehicles will have the relay under the hood, in the long box that houses fuses and relays. Others will have the starter relay attached to the right fender using screws. Sometimes, the starter relay location is under the dash and behind the car stereo. If you cannot find the relay in your vehicle, consult its manual.
For the canister relays, disconnect the battery and other terminals by removing the nuts that hold the leads to the relay. Remove the mounting screws. Fuse box starter relays do not offer any challenge to remove. Their identity is usually indicated on the cover of the fuse box. Use it to locate the position of the starter relay. Then, gently but firmly pull it out.
Note the orientation for the purpose of replacement so you do not install it wrongly after repair. Some starter relays may require a different method to remove, usually taking out mounting screws. Use the appropriate method to remove the component.
Examine the mounting terminals of the relay for corroded parts. Remove the corrosion by scraping it out. If the terminals are set deep like can be the case with a fuse box starter relay, a metal scribe would come in useful.
It is now time to inspect, test, and clean or fix the relay. Check it for signs of corrosion or dirt, especially at the points where an electric current has to flow. Examine the casing for signs melting. After identifying the possible causes of faults from external signs, proceed to the next step.
Start by identifying the kind of starter relay you have in your car. They are usually two types, one with 2 primary connectors and another 4 or more. Testing a two-connector relay is much easy since the primary coil terminals are clearly identifiable.
Once you have determined the starter relay of your vehicle, proceed to the tests. Have your testing tools ready: the battery, multimeter, and jump wires.
Testing a Two-Connector Starter Relay ( the type often mounted on the fender wall)
Note that the terminal polarity does not matter when testing a starter relay. Any can connect to any terminal of the battery, whether negative or positive.
Connect the primary terminals to the battery. Energize the coil by completing the battery connection. Listen for any sound. The relay may produce an audible click. That does not mean it is free from faults. A click can happen, but the contacts may be corroded or burned out and not passing enough current. To get a true picture of the relay’s condition, proceed to step 2.
Set the multimeter to read Ohms or resistance. Connect the probes to the secondary side of the relay. Energize the primary side of the relay by completing the battery’s circuit and read the resistance.
There should be some Ohm reading but not too high. If there is none, the secondary side of the relay is faulty. High resistance or lack of continuity in the secondary circuit when the primary side is energized can indicate burned out contacts. It means a relay that needs replacing.
Take the resistance readings of the primary circuit by connecting the multimeter probes to the small posts. Because of the long coil, the resistance should be somewhat high. However, it should not exceed 5 Ohms. Too high resistance means a bad primary side.
Testing a Four-Connector Starter Relay (the type often found in the fuse box or panel)
The relay usually uses four primary connectors instead of two. To test it, use the following procedure.
Using the multimeter’s Ohm side, identify the connectors that form the primary coil. If you have trouble finding them, use the multimeter. With the knob set to read Ohms, place the multimeter probes on two pins at a time and reading the resistance.
The pins that register a high value should be the coil connections. Check the resistance. It should not exceed 5 Ohms. If it does, the coil side is faulty. Proceed to the next step.
Connect the multimeter to the secondary side of the relay. The pins are distinct and easy to identify.
Read the resistance. It should indicate a small value to show circuit continuity. If the resistance is too high or none at all, the contacts are burnt out or badly corroded, and the relay cannot be used anymore.
How to Fix a Relay
If the relay is corroded or dirt, cleaning the connections can restore the flow of current. Some people will even clean the internal construction of the relay. Most of the time, cleaning the external parts works fine. Use baking soda and wire brush to remove corrosion and dirt. You may also use a blower to remove dirt or microfiber cloth the clean the surfaces of the relay.
Most often, replacing a faulty starter relay is more advisable. With a new relay, you are assured of a problem that is solved once and for all. These components can last for more than a hundred thousand miles. Installing a new one is clearly worth the cost. How do you replace a starter relay? The next chapter explains the process.
How to Replace a Starter Relay
Replacing a starter relay is easy, and almost every vehicle owner can do it. The box-like relay is the easiest to change, while the cylinder type requires a little more work. The hard part when replacing this component is when shopping for one. There are many factors to consider, such as brand, starter relay price, and more. Once you have identified the right relay for your vehicle and purchased it, you only need to know how to install it. Here is how.
Starter Relay Replacement Process
When installing a new starter relay, the steps you follow will depend on its type. Both the removal and mounting processes of the relay are different for the cylinder and box-like starter relays.
How to Properly Remove a Starter Relay
Fuse Box Starter Relay
Open the hood and disconnect the negative terminal of the battery.
Locate the fuse box. It is usually the box with a black lid. If you cannot locate the starter relay, use the manual. With the help of the information on the cover of the fuse box, find the position of the starter relay.
Pull out the starter relay.
Fender Wall Relay
This relay is attached to the fender or firewall. Once you locate it, use the steps below to remove it.
Using a wrench, disconnect the battery terminals.
Next, remove the leads that connect to the terminals of the relay. Use a wrench to remove the nuts that attach the leads to the posts on the relay. There will be four connection points; two big and two small posts.
Remove the screws that mount the relay to the fender and take it out.
How to Install a Starter Relay
Installing a fuse box starter relay is a straightforward process. There are no nuts or screws to fasten and no torque to worry about.
Take your new relay. Matching the pins with their slots in the fuse box, push in the relay, slowly and gently until it reached the end of the seating. Replace the cover and reconnect the battery terminal that you had disconnected when removing the older relay.
To install a fender-mounted starter relay, follow these steps.
Hold the relay against the mounting surface. Insert and fasten the screws that will hold the relay onto the fender wall. Install the battery and starter circuit cables, taking care not to attach the wrong wire to the wrong post. Connect the battery cables that you had removed earlier.
After the installation is complete, test the starting system. The vehicle should have no trouble starting. If it does, check the cables and connections. Ensure the connections are intact and that the fender wall type of starter relay correctly wired. You may check the other parts of the starting system, too, if you cannot diagnose the problem. Or, have a mechanic check the vehicle
How to Wire Starter Relay
A fender mounted starter relay has wires mounted on its connection posts. These leads are usually connected during installation. For the relay to work properly and safely, it needs to be wired correctly. Here is how to wire a typical four-connection starter relay.
Things you will need: pliers, wrenches, and wires ( if they are not provided)
Disconnect the positive battery terminal. Secure the exposed end to avoid accidents. You may use tape to do that.
Find the thick starter solenoid cable. Connect it to one of the big studs or posts on the relay. Secure the connection by tightening the mounting bolt. It does not matter which big terminal you connect the wire to since starter relays do not have polarity.
Get hold of the ignition switch wires. Because they carry a small amount of current, they are usually thinner when compared to the starter cables. Connect one of the two wires to one of the small studs on the relay. Connect the other wire to the remaining small post.
Some relays will only have one small post. If that is the case, connect the ignition wires to the mounting screw or bolt. You can also connect it to anyplace on the relay housing. That is because one of the small terminals of the relay is usually ground.
Connect the remaining thick wire to the only remaining big stud or post. This is the cable connecting to the positive terminal of the battery.
Finally, test the relay wiring by switching on the ignition. The engine should crank and start without any issues. If it fails, check the wiring to ensure every cable is connected to the right terminal and that it is firmly attached.
Starter Relay Replacement Questions
How easy is it to replace a starter relay?
With the right tools and knowledge of what wire to connect to which terminal, the process to change a starter relay should be easy. The fuse box relay is even easier. It usually involves pushing in the new relay after pulling out the old one.
What is the starter relay replacement cost?
Excluding the starter relay cost, expect to pay around $30. Adding the cost to buy the component, the total cost to install a new relay comes to about $50.
How long does a starter relay last?
Typically, expect a starter relay to last more than 100 miles. These components are durable, having only a few moving parts and, therefore, minimal wear. The biggest threat to a starter relays lifespan is usually the contacts burning out.
In vehicles that use starter relays, ensuring that the component is working is critical. It is part of a vehicle’s regular maintenance practices. It can help you avoid starting problems and getting stranded in the middle of nowhere. That starts with knowing how the relay works and how to detect a failing one early enough.
It is our hope that this starter relay guide has provided you with information to help you solve starter relay issues that cause a vehicle to have starting issues. You can now also know what to do, such as removing and testing a bad starter motor. Even replacing a relay whose contacts have burnt out or one that is just too old.