How to Test a 5-Pin Automotive Relay With a Multimeter

 

How to Test a Five-Pin Relay With a Multimeter

You can test a typical five-pin automotive relay by checking its coil resistance, checking the contacts at rest, and then confirming that the contacts switch when the coil receives its rated voltage. First, identify the relay from the terminal numbers or circuit diagram printed on its case. Do not assume that every five-pin relay uses the same internal circuit.

This guide explains the five terminals, the safe multimeter procedure, and what each result means.

Five-pin automotive relay beside a digital multimeter and fused test leads on white paper

What a Five-Pin Automotive Relay Does

An automotive relay is an electrically operated switch. Current through its coil creates a magnetic field that moves an internal armature, which switches a separate load circuit for a horn, fan, lamp, fuel pump, or another device.

A common five-pin relay is a single-pole, double-throw (SPDT) or changeover relay: one common contact switches between two outputs. Some five-pin relays instead use two terminals marked 87. Those dual-87 relays operate differently, so follow the case diagram.

Standard Changeover Terminal Functions

Terminal                        Typical function

85 and 86                       The two ends of the electromagnetic coil

30                                   Common contact for the switched circuit

87                                   Normally open contact; connects to 30 when the coil is                                                       energized

87a                                 Normally closed contact; connects to 30 while the coil is not                                               energized

Cutaway of a five-pin changeover relay showing its coil, armature, and switching contacts

Where the Relay Is Located

Many removable relays sit in an underhood fuse-and-relay box. Others are in an interior fuse panel, behind a trim panel, or near the device they control. The lid diagram, owner's manual, or vehicle service information should identify the correct relay.

Switch the ignition off before removal and pull on the relay body, not its wires. Do not force out solid-state switches or relays built into a control module; this procedure does not cover them.

Removable automotive relay seated among fuses in an underhood electrical box

How a Five-Pin Changeover Relay Works

With the coil off, the return spring holds the moving contact against terminal 87a. Current can pass between 30 and 87a, while 30 and 87 remain open.

When the correct voltage is applied across the coil terminals, the coil's magnetic field pulls the armature. The moving contact leaves 87a and closes against 87. Removing coil power collapses the magnetic field, and the spring returns the contact to 87a. A dual-87 relay is different: both 87 outputs normally close to 30 together when its coil is energized.

Two cutaway views of the same five-pin relay at rest and with its coil energized I

Tools and Safety Before Testing

You need a digital multimeter, relay information, and—only for the powered test—insulated fused jumper leads and a source matching the rated coil voltage. Passenger cars, commercial vehicles, and special applications may differ, so read the case or data sheet.

Remove the relay before using resistance or continuity mode; never measure resistance on an energized circuit. Put the black lead in COM and the red lead in the voltage/ohms jack, then touch the tips together to establish their near-zero reference.

Keep tools away from the battery's opposite terminal and exposed metal. Use an inline fuse close to the power source for any energized test. Stop if the relay or socket is melted, if wiring insulation is damaged, or if the circuit is part of a hybrid or electric vehicle's high-voltage system.

How to Test a Five-Pin Relay With a Multimeter

1. Confirm the Relay Type

Read the small circuit diagram and terminal numbers on the case. A true changeover relay shows 85 and 86 for the coil, 30 as the moving common contact, 87 as normally open, and 87a as normally closed. If the fifth terminal is also marked 87, follow the dual-output diagram instead of the 87a instructions.

If the diagram or part number is unreadable, do not apply power randomly. A polarity-sensitive suppression diode may be hidden across the coil, and reversed power can damage it or create a short. Look up the exact relay instead.

2. Inspect the Relay and Terminals

Look for heat discoloration, melted plastic, loose blades, corrosion, or a burnt odor. Heat damage means the socket and connected load also need inspection; a new relay alone may not correct the cause.

3. Check the Coil Between 85 and 86

Set the meter to resistance (Ω). Touch one probe to 85 and the other to 86 without letting the probe tips touch each other. A stable, finite reading shows that the coil has an electrical path. “OL” or an infinite reading usually indicates an open coil.

Do not judge the coil from one universal ohm range. Coil resistance varies with relay design, rated voltage, temperature, and built-in suppression components. Compare the reading with the manufacturer's data or an identical known-good relay. A reading extremely close to the shorted-lead reference may indicate a shorted coil, but confirm it against the correct specification.

4. Check the Contacts With the Coil Off

Switch the meter to continuity or low resistance. On a standard changeover relay at rest:

  • 30 to 87a should show a closed path.

  • 30 to 87 should show an open path.

  • 87 to 87a should remain open.

A closed contact may beep or read close to the resistance of the test leads. The exact continuity-beeper threshold depends on the meter. A beep is a quick screening result, not a measurement of how the contact will behave under its normal electrical load.

Multimeter probes checking the closed resting contacts inside a five-pin relay I

5. Apply the Rated Coil Voltage and Verify the Switch

Perform this step only when you know the relay's rated coil voltage and polarity requirements. Connect the fused positive jumper and negative jumper to the correct coil terminals shown on the relay diagram. On many unsuppressed or resistor-suppressed coils, polarity is not critical. A relay with a built-in diode is polarity-sensitive, so follow its printed symbol or data sheet exactly.

The relay should make a clear click as the armature moves, but the click alone does not prove that the contacts conduct correctly. Keep the coil energized only long enough to take the test readings. For a changeover relay:

  • 30 to 87 should now show a closed path.

  • 30 to 87a should now show an open path.

Disconnect the coil power. The contacts should return to their resting state. If you cannot make secure fused connections without the jumpers touching neighboring terminals, stop and use a relay test socket or ask a qualified technician to perform the powered test.

Fused low-voltage supply energizing a five-pin relay while a multimeter checks its switched contacts

How to Interpret the Results

The relay likely passes if its coil resistance is plausible for that part, its resting contacts match the diagram, and both contact states switch and return consistently.

An open coil, contacts that do not change state, or a closed contact with unusually high resistance compared with the meter leads may indicate relay failure. Intermittent results can come from worn contacts, internal mechanical wear, loose test connections, or corrosion.

A bench test does not prove that the vehicle circuit is good. Continuity mode uses little current, so pitted contacts may pass it yet cause voltage drop under load. The socket may also lack power, ground, or a control signal. Those checks require a wiring diagram and live-circuit testing.

Hand-drawn comparison of clean closed relay contacts and worn heat-discolored contacts

If the Relay Passes but the Component Still Does Not Work

A good relay cannot operate the load if a fuse is open, a socket terminal is damaged, the coil lacks a control signal or ground, wiring is faulty, or the load itself has failed.

Do not bridge high-current relay-socket terminals unless the vehicle's service procedure specifically allows it and you understand the circuit. A wrong jumper can damage wiring or an electronic control module. For a beginner, the safer next step is to inspect the correct fuse and socket visually, then use a wiring diagram or seek professional diagnosis.

When to Stop and Contact a Mechanic

Stop if the fuse repeatedly opens, the relay or socket becomes hot, plastic is melted, wiring conflicts with service information, or the controlling module is unknown. Seek help for intermittent faults under load or while driving.

Do not work on orange high-voltage cables or high-voltage battery contactors in a hybrid or electric vehicle. The five-pin low-voltage relay procedure in this article does not apply to those systems.

Replacement and Installation Tips

Match the original part number, terminal arrangement, coil voltage, contact ratings, suppression type, and physical keying. Relays fitting the same socket can have different circuits.

An identical known-good relay may be swapped temporarily only when the part numbers and diagrams match and the other circuit is not safety-critical. Inspect a heat-damaged relay's socket and load before replacement.

15. Frequently Asked Questions

Can a five-pin relay click and still be bad?

Yes. The click confirms that the armature moved, but worn or pitted contacts may still have excessive resistance. Check the contact states with the multimeter and investigate voltage drop under load if the vehicle problem remains.

What should the resistance be between terminals 85 and 86?

There is no single correct value for every relay. Coil resistance depends on the relay design, rated voltage, temperature, and suppression circuit. A finite stable reading is a useful first check, but compare it with the manufacturer's specification or an identical relay.

Should terminals 30 and 87a have continuity?

On a standard five-pin changeover relay, 30 and 87a are normally connected while the coil is off. They should separate when the coil is energized. Confirm that the case actually identifies the fifth terminal as 87a.

Does polarity matter on terminals 85 and 86?

It can. A relay with a built-in suppression diode is polarity-sensitive. Follow the polarity shown on its case or data sheet. An unsuppressed or resistor-suppressed coil may not be polarity-sensitive, but the manufacturer's diagram remains the authority.

Is every five-pin automotive relay an SPDT relay?

No. A common five-pin relay is SPDT and uses 87a, but some five-pin models have two normally open 87 outputs. Others may use a manufacturer-specific layout. Read the terminal markings and schematic before testing.

Can I test the relay without applying power to the coil?

You can check the coil for an open circuit and verify the resting contacts without powering it. To confirm that the armature switches between 87a and 87, you normally need the correct rated coil voltage or a suitable relay tester.

16. Conclusion

To test a five-pin relay with a multimeter, begin with the diagram on the case. Check the coil between 85 and 86, verify the resting paths from 30 to 87a and 87, then apply the correct fused coil voltage and confirm that those paths switch. Treat coil resistance as relay-specific, observe diode polarity, and remember that a passing bench test does not rule out a faulty fuse, socket, control circuit, or electrical load.