How to test a Relay

In this video I explain how to test a relay using a multi-meter and a square battery.

The terminals of a relay are numbered using an identification system known as DIN 72552. This system was developed in the German automotive industry and has since been adopted across the world as the standard method for labelling and identifying electrical terminals. DIN 72552 assigns a numeric code that clearly defines the function of each pin/ terminal in a relay. The table below shows the codes used in automotive relays.

85 Relay Coil Negative
86 Relay Coil Positive
87 Common Contact - Output
87a Normally Closed Contact (NC) - Output
87b Normally Open Contact (NO) - Output
88 Common Contact 2 - Output
88a Normally Closed Contact 2 - Output
88b Normally Open Contact 2 - Output
30 Feed/ Line In Positive

A micro relay is a smaller version of the more popular standard relay and are used when space is at a premium. Micro relays are more compact than the standard size and are an ideal choice when you need to save space - for example in an ATM fuse box set up with mini fuses. They have a smaller rectangular shape compared to the square cubed shape of the standard relay. Micro automotive relays use a different terminal number identification system compared to standard mini relays. See the list below for micro relay terminal numbering:

1: (4.8mm) Coil Positive
2: (4.8mm) Coil Negative
3: (6.3mm) Feed/ Line In Positive
4: (4.8mm) Normally Closed (NC) - Output
5: (6.3mm) Normally Open (NO) - Output


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