{"id":32646,"date":"2026-10-08T07:58:31","date_gmt":"2026-10-08T14:58:31","guid":{"rendered":"https:\/\/digilent.com\/blog\/?p=32646"},"modified":"2026-10-08T07:58:31","modified_gmt":"2026-10-08T14:58:31","slug":"how-to-test-a-relay-with-a-multimeter","status":"publish","type":"post","link":"https:\/\/digilent.com\/blog\/how-to-test-a-relay-with-a-multimeter\/","title":{"rendered":"How to Test a Relay with a Multimeter: A Detailed Guide"},"content":{"rendered":"

How to Test a Relay With a Multimeter: A Detailed Guide<\/span><\/h1>\n

A multimeter tests a relay in two ways. First, set it to ohms (\u03a9) mode and measure the coil resistance, which should read 50-120 \u03a9 on most 12 V relays. Then switch to continuity mode and confirm the contacts open and close correctly when the coil is energized versus de-energized.<\/span><\/p>\n

A relay that won’t switch can shut down everything from a car’s fuel pump to a bench-top automation project. The good news is you don’t need specialized gear to diagnose one. <\/span>A multimeter<\/span><\/a> with resistance, continuity, and diode modes can tell you whether a relay is healthy, dead, or hiding an intermittent fault, usually in under five minutes.<\/span><\/p>\n

The same basic test works whether you’re checking a relay on the bench or chasing a no-start problem in a car. Solid-state relays work differently, but you can test those with a multimeter too, using one additional diode-mode check.<\/span><\/p>\n

What is a relay and how does it work?<\/span><\/h2>\n

A relay is an electrically operated switch. Current flowing through a coil creates a magnetic field that pulls a movable armature. That armature closes (or opens) a separate set of contacts, letting a low-power signal switch a much larger load.<\/span><\/p>\n

Inside a standard electromechanical relay, you’ll find four key parts. There’s a coil, an armature, a spring, and a contact set.<\/span><\/p>\n

When current flows through the coil, it becomes an electromagnet and pulls the armature against the spring’s tension, switching the contacts. Cut the power, and the spring returns the armature to its resting position.<\/span><\/p>\n

The magic here is isolation. A tiny current, often just a few milliamps from a microcontroller or a switch on your dashboard, can control circuits carrying many amps.<\/span><\/p>\n

Relays show up everywhere, from car electrical systems to industrial control panels. If you want to see this in action, try a <\/span>hands-on relay project<\/span><\/a> that uses a relay to switch between two LEDs.<\/span><\/p>\n

Normally open (NO) vs normally closed (NC) contacts<\/span><\/h3>\n

At rest, with no power applied to the coil, the armature sits against the normally closed (NC) contact. Energizing the coil moves it to the normally open (NO) contact. This is the switching behavior you’ll check during the continuity test.<\/span><\/p>\n

Automotive relays use standardized pin numbers, and 85 and 86 are the coil terminals:<\/span><\/p>\n