Testing a 5 pin relay with a multimeter is one of the most important skills for anyone working with electrical circuits in cars, home appliances, or industrial systems. Relays are small but powerful devices that let you control large currents with a small electrical signal. When a relay fails, it can cause anything from a headlight not working to a motor refusing to start. Many people replace relays without checking them, which wastes money and time. Learning to test a 5 pin relay with a multimeter not only saves you from guessing but also gives you confidence in your repairs.
This guide will take you through every step you need to know. You’ll understand what a 5 pin relay is, why they are used, and how each pin works. We’ll look at the tools you need, safety tips, and the most reliable methods to test the coil, contacts, and switching function.
You’ll find out how to read relay pinouts, spot common mistakes, and use your multimeter correctly for each test. Even if you’re new to electronics, you’ll finish with practical knowledge you can use right away. Let’s dive in and make relay testing simple and effective.
Understanding The 5 Pin Relay
A 5 pin relay is an electromechanical switch with five terminals. It is widely used in automotive and industrial circuits to control a high-power device using a low-power signal. What makes it special compared to a 4 pin relay is the extra pin, which allows for a normally closed (NC) and a normally open (NO) contact. This means the relay can switch between two output circuits, providing more flexibility.
The main components inside a relay include a coil (which creates a magnetic field when energized) and a set of contacts (which open or close the circuit). The five pins are typically:
- Coil Pin 1 – one end of the coil
- Coil Pin 2 – the other end of the coil
- Common (COM) – the moving part that connects to either output
- Normally Open (NO) – disconnected when the relay is off, connected when energized
- Normally Closed (NC) – connected when the relay is off, disconnected when energized
Relays are used in car starters, fuel pumps, home automation, and industrial machines. Knowing how to test all five pins gives you a complete picture of relay health.
Tools And Preparation
Before you start testing, you need the right tools and to understand basic safety.
- Digital Multimeter: Choose one with both resistance (ohms) and continuity testing.
- Relay Diagram or Pinout: Check the relay body or manufacturer’s datasheet.
- 12V Power Source: Optional, for function testing.
- Insulated Gloves: For safety, especially around automotive or high-voltage relays.
- Screwdriver or Test Leads: To connect and hold wires.
Check your multimeter batteries and ensure your test leads are in good condition. Identify each relay pin from the diagram, since mixing up pins can lead to wrong readings or even damage.
How A Multimeter Helps
A multimeter is your main tool for relay testing. It measures resistance, voltage, and continuity. For relays, you mostly use the resistance (ohms) setting and the continuity buzzer. Some advanced multimeters can also test diodes, but that is less common with 5 pin relays.
A key point many beginners miss: before testing, always set the multimeter to the correct range. For relay coils, resistance is usually between 50 and 200 ohms. Setting the range too high or low may give confusing results.
The 5 Steps To Test A 5 Pin Relay With A Multimeter
Testing a 5 pin relay involves five main checks. Each focuses on a different pin or function. Let’s go through each in detail.
1. Identify The Pins And Read The Pinout
Every relay has a different pin arrangement, so your first job is to identify each pin correctly. Many relays have numbers like 85, 86, 30, 87, and 87a molded into the plastic.
- 85 and 86: Relay coil (connects to the control circuit)
- 30: Common terminal
- 87: Normally open (NO)
- 87a: Normally closed (NC)
If your relay has a diagram, use it to double-check. If not, search the manufacturer’s site or a trusted electronics resource.
Key Tip
Many beginners guess the pins or trust wire colors, which can be wrong. Take time to confirm before you start testing.
2. Testing The Coil Resistance
The coil is the heart of the relay. If the coil is open (broken wire) or shorted, the relay will not work. To test:
- Set your multimeter to the resistance (ohms) mode.
- Place the probes on pins 85 and 86 (the coil pins).
- Note the reading.
A typical 12V relay coil should read between 50 and 200 ohms. If you see infinite resistance (OL), the coil is open and the relay is bad. If you see zero or very low resistance (less than 10 ohms), the coil may be shorted.
| Coil Resistance (Ohms) | Status | Relay Condition |
|---|---|---|
| 50–200 | Normal | Good |
| 0–10 | Shorted | Faulty |
| OL/∞ | Open | Faulty |
Common Mistake
Some people measure across the wrong pins, leading to confusing readings. Always confirm you’re on the coil pins.
3. Testing The Normally Closed (nc) Contact
The NC contact (often pin 87a) should be connected to the common terminal (pin 30) when the relay is not energized.
- Set your multimeter to continuity or low resistance.
- Place one probe on pin 30 and the other on pin 87a.
- The meter should beep (continuity) or show near zero ohms.
If there is no continuity or the resistance is very high, the NC contact is faulty. This is important in circuits where the relay needs to pass current when “off. ”
Non-obvious Insight
Some relays have dirty or oxidized contacts, causing intermittent faults. If the reading jumps or fluctuates, try gently tapping the relay. If it improves, the relay may work now but can fail soon. Replace it.
4. Testing The Normally Open (no) Contact
The NO contact (often pin 87) should be disconnected from the common terminal (pin 30) when the relay is not energized.
- Set your multimeter to continuity or resistance.
- Place one probe on pin 30 and the other on pin 87.
- The meter should show no continuity (infinite resistance).
If you see a connection here, the relay is stuck or shorted. This can cause devices to stay on when they should be off.
Practical Example
In a car’s fuel pump relay, a stuck NO contact can keep the pump running even with the ignition off. This drains the battery and can be dangerous.
5. Energizing The Relay And Testing The Switching Function
This is the most complete test and the step many skip. Here, you apply power to the coil and check if the relay switches correctly.
- Connect a 12V power supply to the coil pins (85 and 86).
- While energized, measure continuity between pin 30 and pin 87 (NO).
- You should now have continuity or low resistance.
- Measure between pin 30 and pin 87a (NC).
- There should be no continuity.
This proves the relay can actually switch under real conditions.
| Relay Coil Energized? | 30–87 Continuity | 30–87a Continuity |
|---|---|---|
| No | No | Yes |
| Yes | Yes | No |
Advanced Tip
Some relays “click” audibly when energized. If you hear the click but the contacts don’t switch, the relay is defective. Mechanical movement is not a guarantee of good electrical function.
Credit: en.50factory.com
Comparison: 4 Pin Vs 5 Pin Relays
To clarify why 5 pin relays are different, here’s a quick comparison:
| Feature | 4 Pin Relay | 5 Pin Relay |
|---|---|---|
| Number of Contacts | 1 (NO) | 2 (NO & NC) |
| Flexibility | Less | More |
| Common Uses | Simple switching | Changeover, advanced control |
Troubleshooting Common Relay Problems
Even with good test results, relays can sometimes fail in the field. Here are issues to watch for:
- Intermittent operation: May pass bench tests, but fail under vibration or heat. Replace if you see inconsistent readings.
- Contact arcing: Burnt or pitted contacts may work now but fail soon. Inspect for dark spots or melted plastic.
- Wrong pin wiring: Double-check connections, especially if relay doesn’t fit the socket or works backwards.
If a relay passes all the above tests but the circuit still fails, look for broken wires, blown fuses, or corroded connectors.
Practical Safety Tips
- Always disconnect power before removing or testing relays in live circuits.
- When testing in a car, avoid touching metal parts with bare hands.
- Mark tested relays so you don’t confuse good and bad parts.
- Never force probes into relay sockets; use proper test leads.
Electrical burns and short circuits are real dangers. Take your time and stay alert.
Real-world Example
Imagine your car’s headlights only work sometimes. You suspect the relay. Following the steps above:
- You identify the 5 pin relay and check the pinout.
- The coil reads 120 ohms – good.
- The NC contact shows continuity.
- The NO contact is open when off, and closes when the relay is energized with 12V.
- But, when you tap the relay, the NO contact sometimes fails.
This points to worn contacts inside. Even though the relay almost passed, you replace it and the headlights work perfectly. This shows why thorough testing is important.
Credit: www.kynix.com
What Not To Do
Some common mistakes to avoid:
- Skipping the pinout check: Wrong connections can damage both the relay and your multimeter.
- Testing only one contact: A relay might have one good and one bad contact.
- Ignoring coil resistance: A shorted coil can blow fuses and damage circuits.
- Testing in-circuit: Always remove the relay for accurate results unless you are sure about the circuit layout.
How To Store And Handle Relays
- Keep relays in dry, dust-free containers.
- Label relays with test results if saving for later.
- Avoid dropping or exposing relays to heat, as this can damage the internal mechanism.
When To Replace A Relay
Replace a 5 pin relay if:
- The coil is open or shorted.
- Any contact fails the continuity test.
- The relay clicks but doesn’t switch.
- You see physical damage, melted parts, or a burnt smell.
- Testing shows intermittent or unstable readings.
Relays are not expensive, but a failed relay can cause big problems. If in doubt, swap with a known good relay.
Where To Learn More
The best way to master relay testing is by practicing on real relays from old cars or appliances. Schematics and pinouts are often available on manufacturer websites or trusted electronics sources like Wikipedia.
Credit: m.youtube.com
Frequently Asked Questions
How Do I Know Which Pin Is Which On A 5 Pin Relay?
Most relays have a diagram printed on the side, showing numbers like 85, 86, 30, 87, and 87a. You can also find the pinout in the datasheet. If not, use a continuity test to identify the coil pins (which will show resistance, not continuity to other pins).
Can I Test A Relay Without Removing It From The Circuit?
You can do some tests in-circuit, but for accurate results, especially when checking coil resistance and contact function, it’s best to remove the relay. Other connected devices may affect your readings.
What Does It Mean If The Relay “clicks” But Still Doesn’t Work?
A click means the coil is working, but the contacts may be dirty, pitted, or stuck. Test for continuity while the relay is energized. If there is no continuity where there should be, replace the relay.
How Long Does A Typical Relay Last?
Automotive relays are rated for thousands to hundreds of thousands of cycles. However, high current, heat, or vibration can shorten lifespan. If you see intermittent problems, replace the relay even if it passes basic tests.
Is It Possible To Repair A Faulty Relay?
Most relays are sealed and not meant to be repaired. Opening them can damage the mechanism and is not recommended. In rare cases, cleaning contacts may help, but it’s safer and faster to replace the relay.
Testing a 5 pin relay with a multimeter is a simple but essential skill. With the right steps, you can quickly find faults, save money, and keep your electrical systems running safely. Each check builds your confidence and helps you become more skilled with real-world electronics.