How to test the ignition switch with a multimeter
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Are you trying to start your car and the engine just won't move?
If so, then the problem may not be the engine, but the culprit, which is usually not studied like other components of the car.
This is your ignition switch.
The ignition switch is an electrical component, usually located on the steering wheel, that turns the car on.
If it's faulty, you don't expect your engine or electrical accessories to turn on.
Not many people know how to diagnose this electrical component, which is why we are here to help.
We will show you 6 proven ways to check the ignition switch with a multimeter.
Let's get started.
Symptoms of a faulty ignition switch
There are many signs in cars that serve as pointers to a faulty ignition switch.
Along with your car not starting, some other symptoms of a bad ignition switch include:
- Difficulty removing or turning the ignition key, indicating wear on the ignition switch. It may also indicate that the dongle is not connected properly inside the switch.
- Engine still running after ignition off and key removed
- Stopping the car while driving, which could be caused by a loss of engine power through the switch.
- Car accessories do not work even when the ignition key is turned to the working position
- The ignition switch is hot when you touch it. This indicates a malfunction in the electrical system.
If you are experiencing one or more of these symptoms, the ignition switch may be the cause and needs to be replaced.
When testing electrical components, a multimeter is a valuable tool.
How to test the ignition switch with a multimeter
Turn the key on, set the multimeter to 20 VDC, ground the black wire to any metal nearby, and connect the red wire to the connector on the opposite side of the ignition cylinder. If the multimeter shows a reading far from your battery voltage, the switch is faulty..
There is more to this process, as well as other methods you can use to diagnose your ignition switch.
Step 1: Remove the cover under the steering wheel
To test the ignition lock with the first method, you need to remove the casing that covers other parts of the switch.
It's a shroud located under the steering wheel and you remove it to expose the metal connectors on the other end of the switch.
Step 2 Set the multimeter to the 20 VDC voltage range.
Your vehicle uses direct current (DC voltage) and your battery voltage is taken into account in this test.
At voltages typically around 12 volts, you set the multimeter's dial to the 20 VDC voltage range, as this ensures accurate readings.
DC voltage is usually represented by the letter "V" with a dash and three dots next to it.
Step 3: Place the multimeter leads on the car and the ignition switch
Ground the black (negative) test lead to any metal part of the vehicle. It could be a screw nearby or even the body of your car.
Place the red (positive) test lead on any of the metal connectors on the other side of the ignition switch.
This is the opposite end of the switch cylinder that the wires are connected to, and they are important when checking if the ignition switch is passing current or not.
Step 4. Turn on the ignition and evaluate the results.
Now you turn the key to the working position without trying to start the engine and check what the multimeter shows you.
A reading close to your battery voltage means the ignition switch is working properly.
For example, if you are using a 12 volt battery, the 11 volt reading is still significant and means the ignition switch is working properly.
If the multimeter shows you 0 or readings far from this range, then the ignition switch is faulty and needs to be replaced.
Method 2: Checking the fuse and battery
Step 1: Open the fuse panel under the steering wheel
The second method also involves opening the cover under the steering wheel.
This is to expose the starter fuse, not the metal connectors on the other end of the switch.
Step 2: Remove the starter signal fuse.
Now you use your fuse pullers to remove the starter signal fuse from the port it is plugged into.
Step 3: Inspect the fuse
Inspect the metal strip on the fuse to make sure it is in good condition.
If you suspect damage, simply replace this component with a new one of the same amperage. Make sure this new fuse actually works.
Step 4: Battery Cross Check
You also check that your battery is not damaged, and a multimeter will help you here.
Ground the multimeter's black test lead to any metal nearby (possibly the body of a car), and then place the red test lead to the positive battery terminal.
If the multimeter shows nothing close to 12 volts, it needs to be replaced.
Once you replace it, or if it's still in good condition, move on to the next step.
Step 5: Turn on the ignition and evaluate the results
The last step is to turn the ignition key back to its original position and see if the engine starts.
If, after replacing these components, the engine starts, then they were the culprits.
If the engine won't start but you hear a click when you turn the key, then your ignition switch is working properly and the problem is elsewhere.
If the engine won't start and you don't hear a click, then your ignition switch is faulty and needs to be replaced.
Method 3: check with spark plugs
Locate the spark plug in the engine and disconnect one of the wires connected to it.
Insert the old spark plug into the tip of the spark plug, and then place the metal part of the spark plug on any metal surface near you.
Start the engine and look for a spark on the old spark plug (you can have a helper do this for you).
If you don't see a spark, the ignition switch may be faulty and you need to replace it.
Method 4: Ignition Coil Test
You can also test your vehicle's ignition coil.
When your multimeter is set to DC voltage, you place the red test lead on the positive coil terminal and the black test lead on the negative terminal of your battery.
Turn the key to the "on" position without starting the engine and check what the multimeter shows you.
It is expected that with a good ignition system, the multimeter will output about 12 V.
If the multimeter doesn't show a value close to this, or you don't get any readings at all, your ignition switch, wiring, or coil may be faulty and need to be replaced.
Method 5: Testing with the ignition module
There are two tests you can perform with your ignition module.
In the first step, connect the black probe of the multimeter to the negative terminal of the battery, and the red probe to the positive terminal of the ignition module.
Turn the key to the on position without starting the engine and see what the multimeter shows.
If you don't get any reading, then there may be an open circuit between the ignition module wire and your switch.
The second test additionally involves using your distributor.
You remove the distributor cap, place the black lead of the multimeter on the negative battery terminal, and the red lead of the multimeter on the negative wire of the ignition module.
Rotate the middle distributor shaft and see what the multimeter shows. If your ignition switch and distributor are working properly, the multimeter is expected to read zero (0).
If you are getting a multimeter reading, there may be a problem with the ignition switch wiring and you are looking for how to replace it.
Method 6: Ignition Switch Continuity Check
The last diagnostic is to check the integrity of the ignition switch circuit. Here you completely separate the ignition lock from any other add-on.
The ignition switch usually has five terminals.
- Earth (G)
- Magneto (M)
- Breakfast)
- Light (L) and
- Battery (B)
Set the multimeter to continuous or ohms mode and record these positions for the placement of the multimeter leads.
If you place the black probe on the metal body of the switch and the red probe on the "G" terminal, there should only be a circuit when the switch is off.
When you place the black probe on the "G" terminal and the red probe on the "M" terminal, you also only expect continuity when the switch is off.
Now, with the "B" and "L" terminals, you only expect continuity when the switch is turned to the "on" position.
This means that while the switch is off, the multimeter should be silent or show "OL".
Between the "B" and "S" terminals, you only expect continuity when the switch is in the "start" position. This means that it is expected to be silent when it is in the "off" and "on" positions.
If this is confusing, here is a video that shows you how to perform an ignition switch integrity test.
Conclusion
There are several methods for checking the health of the ignition switch.
However, the first and last methods are best for directly determining if your ignition switch is working.
Other tests help diagnose other ignition system components that may be additional culprits.
F.A.Q.
How to bypass the ignition lock?
Connect the positive terminal of the ignition coil and the starter wire to the positive terminal of the battery. Disconnect the switch wire from the solenoid and directly connect the red cable on the solenoid to this location.
How can I start my car without an ignition lock?
Remove the cover under the steering wheel and locate the brown starter wires and red battery wires. Twist the red wires together and then touch the brown wires to start the engine.
Can a faulty ignition switch drain a battery?
A bad ignition switch only drains a car battery when it fails to turn off the car. It can also discharge slowly if you repeatedly try to start the car without success.
Alex Klein is an electrical engineer with over 15 years of experience. He is the host of the Electrouniversity YouTube channel, which has thousands of subscribers.
