Testing a relay with a multimeter is a reliable way to check if it's functioning properly. Below is a step-by-step guide to testing both the coil (control side) and the contacts (switched side) of a standard automotive or electrical relay.

Tools Needed:

• Digital multimeter (set to Ohms Ω and continuity/diode mode)

• 12V power source (car battery or external supply for energizing the relay)

• Jumper wires (optional, for activating the relay)

Step 1: Identify Relay Terminals

Most relays have 4 or 5 pins, labeled as:

• 85 & 86 → Coil (electromagnet that activates the relay)

• 30 → Common (input from power source)

• 87 → Normally Open (NO) (connects to 30 when relay is powered)

• 87a → Normally Closed (NC) (only in 5-pin relays, disconnects when relay is powered)

Step 2: Test the Relay Coil (Terminals 85 & 86)

1. Set multimeter to Ohms (Ω) mode.

2. Place probes on terminals 85 & 86.

• ∞ (OL) = Open circuit → Coil is broken.

• 0Ω or very low → Coil is shorted.

• Good relay: Should read 50–120Ω (varies by relay).

• Bad relay:

✅ If resistance is within range, the coil is OK.

Step 3: Test Normally Open (NO) Contacts (Terminals 30 & 87)

1. Set multimeter to continuity (beep) mode.

2. Check terminals 30 & 87 without power:

• Should be open (no continuity, no beep).

3. Apply 12V to terminals 85 (+) & 86 (-) to energize the relay.

• Use a car battery or power supply.

4. Recheck terminals 30 & 87:

• Should now show continuity (beep).

• If not, the contacts are faulty.

Step 4: Test Normally Closed (NC) Contacts (Terminals 30 & 87a) – (5-Pin Relays Only)

1. Set multimeter to continuity mode.

2. Check terminals 30 & 87a without power:

• Should show continuity (beep).

3. Apply 12V to 85 & 86 to energize the relay.

4. Recheck terminals 30 & 87a:

• Should now be open (no beep).

• If not, the NC contacts are stuck.

Step 5: Check for Voltage Drop (Optional)

• Energize the relay (12V to 85 & 86).

• Set multimeter to DC voltage (20V range).

• Measure voltage between 30 (input) & 87 (output).

• Good relay: < 0.5V drop.

• Bad relay: High voltage drop (poor contact).

Summary of Relay Test Results:

Troubleshooting Tips:

• No click when powered? → Coil is dead (check resistance).

• Clicks but no continuity? → Contacts are burnt/corroded.

• Works intermittently? → Internal arcing or weak coil.

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