Disconnect the relay from power
Identify the relay coil terminals and switch terminals using the relay diagram
Inspect the relay for visible damage, corrosion, or burnt contacts
Set a multimeter to measure resistance
Measure coil resistance across the coil terminals
Compare the reading to the relay’s specified coil resistance
Check for an open coil if the meter shows infinite resistance
Check for a shorted coil if the resistance is unusually low
Apply the rated coil voltage to the relay
Listen and feel for a click when the relay energizes
Measure continuity across the normally open contacts with the relay de-energized
Measure continuity across the normally closed contacts with the relay de-energized
Measure continuity across the normally open contacts with the relay energized
Measure continuity across the normally closed contacts with the relay energized
Verify contact resistance is very low when closed
Verify contacts open and close reliably during repeated tests
Test the relay under load if possible
Replace the relay if it fails any test