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How To: Test a Relay


BigRondo

USMC 1371
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Year, Model & Trim Level
2002 XLT V6 4x4
I noticed that several people have been asking how to test a relay lately, so I worked this up. Enjoy.

Be sure to check out my other write-ups:

How To: Replace Blend Door Actuator in 3rd Gen Ex

How To: Remove/Replace 3rd Gen Door Panel

How To: Install Signal Mirrors On 3rd Gen Ex

How To: Restore Faded, Yellowing Headlights

How To: Replace Multifunction Switch in 3rd Gen Ex

How To: Paint Rear Pillar Trim

How To: Replace 3rd Gen Ambient Air Temperature Sensor

How To: Remove/Replace 3rd Gen Center Console



Here is a basic automotive relay:

RelayWiringGuide.jpg


With no power on the coil there is a connection between pins 30 & 87a (closed), and no connection between pins 30 & 87 (open), as shown in the picture.

When power is applied to the coil (pins 86 & 85), there is a connection between pins 30 & 87 (closed), and no connection between pins 30 & 87a (open).

To test the relay, disconnect all wiring or remove it from it's socket. For the tests listed below, the meter will be set on Continuity/Resistance.

ContinuityResistance.jpg


Step 1 is to test the Coil:

  • Set the meter on Continuity/Resistance
  • Test the continuity between terminals 85 & 86
    • If meter measures Continuity/Resistance, the Coil should be good
    • If the meter measures No Continuity/Resistance, the Coil is bad and the relay should be replaced

Step 2 is to test the Normally Closed Terminals :

  • Set the meter on Continuity/Resistance
  • Test the continuity between terminals 30 & 87a
    • If meter measures Continuity, the Normally Closed Function of the relay should be good
    • If the meter measures No Continuity, the Normally Closed Function of the relay is bad and the relay should be replaced

Step 3 is to test the Normally Open Terminals :

  • Set the meter on Continuity/Resistance
  • Test the continuity between terminals 30 & 87
    • If meter measures No Continuity, the Normally Open Function of the relay should be good
    • If the meter measures Continuity, the Normally Open Function of the relay is bad and the relay should be replaced

If at this point the relay has proven to be good, The next step is to test that it functions properly when the coil is energized.

Step 4 is to test the Actual Function of the Relay :

  • Set the meter on Continuity/Resistance
  • Connect one probe from the meter to Terminal 30 on the relay
  • Connect the other probe to Terminal 87 on the relay
    • At this point the meter is reading No Continuity
  • Connect Terminal 85 to the Negative on the Battery
  • Connect Terminal 86 to the Positive on the battery
    • At this point the Coil is energized
    • The meter should be reading Continuity
      • If the meter is reading Continuity, the relay is good!
      • If the meter is reading No Continuity, the relay is bad and should be replaced

Hope this helps out and didn't confuse you too much! :D:thumbsup:
 




raffeysod

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November 15, 2014
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1997 Explorer 5.0L V8
Great info. Thanks for the tutorial.

I noticed that several people have been asking how to test a relay lately, so I worked this up. Enjoy.

Be sure to check out my other write-ups:

How To: Replace Blend Door Actuator in 3rd Gen Ex

How To: Remove/Replace 3rd Gen Door Panel

How To: Install Signal Mirrors On 3rd Gen Ex

How To: Restore Faded, Yellowing Headlights

How To: Replace Multifunction Switch in 3rd Gen Ex

How To: Paint Rear Pillar Trim

How To: Replace 3rd Gen Ambient Air Temperature Sensor

How To: Remove/Replace 3rd Gen Center Console



Here is a basic automotive relay:

RelayWiringGuide.jpg


With no power on the coil there is a connection between pins 30 & 87a (closed), and no connection between pins 30 & 87 (open), as shown in the picture.

When power is applied to the coil (pins 86 & 85), there is a connection between pins 30 & 87 (closed), and no connection between pins 30 & 87a (open).

To test the relay, disconnect all wiring or remove it from it's socket. For the tests listed below, the meter will be set on Continuity/Resistance.

ContinuityResistance.jpg


Step 1 is to test the Coil:

  • Set the meter on Continuity/Resistance
  • Test the continuity between terminals 85 & 86
    • If meter measures Continuity/Resistance, the Coil should be good
    • If the meter measures No Continuity/Resistance, the Coil is bad and the relay should be replaced

Step 2 is to test the Normally Closed Terminals :

  • Set the meter on Continuity/Resistance
  • Test the continuity between terminals 30 & 87a
    • If meter measures Continuity, the Normally Closed Function of the relay should be good
    • If the meter measures No Continuity, the Normally Closed Function of the relay is bad and the relay should be replaced

Step 3 is to test the Normally Open Terminals :

  • Set the meter on Continuity/Resistance
  • Test the continuity between terminals 30 & 87
    • If meter measures No Continuity, the Normally Open Function of the relay should be good
    • If the meter measures Continuity, the Normally Open Function of the relay is bad and the relay should be replaced

If at this point the relay has proven to be good, The next step is to test that it functions properly when the coil is energized.

Step 4 is to test the Actual Function of the Relay :

  • Set the meter on Continuity/Resistance
  • Connect one probe from the meter to Terminal 30 on the relay
  • Connect the other probe to Terminal 87 on the relay
    • At this point the meter is reading No Continuity
  • Connect Terminal 85 to the Negative on the Battery
  • Connect Terminal 86 to the Positive on the battery
    • At this point the Coil is energized
    • The meter should be reading Continuity
      • If the meter is reading Continuity, the relay is good!
      • If the meter is reading No Continuity, the relay is bad and should be replaced

Hope this helps out and didn't confuse you too much! :D:thumbsup:
 




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