Automotive Relay Product Guide
Automotive relays come in many shapes and forms. The most basic consisting of an electromagnetic switch.
The term "relay" is sometimes also used to describe small electronic controllers such as glow plug controllers etc. which also contain electronic circuits
.

Function

Typical terminal designation

Operation

Normally Open 4 pin  relay

NO_Relay.jpg

12v 20A 4 pin relay
12v 30A relay with detachable bracket 12v 30A relay with inc blade fuse
12v 40A relay NO 4 pin
12v 70A heavy duty 4 pin relay

24v 20A 4 pin NO relay

 
30 Supply Input
87
Supply Output
85
Coil ground or -ve
86
Coil trigger

A control circuit between pins 85 & 86 eg, with light duty control switch and wiring , may be used to switch a second circuit with heavier current load via wiring between pins 30 and 87

Heavy Duty Automotive Relay 12v 200A relay
30 Supply Input
87
Supply Output
85
Coil ground or -ve
86
Coil trigger

Normally open relay often used on construction plant for starter circuit control

Double Make & Break
30 Supply Input
87
Supply Output(1)
87b
Supply Output(2)
85
Coil ground or -ve
86
Coil trigger

Similar operation to the standard 4 pin Normally Open relay but has a second terminal in parallel to the output terminal.

Changeover Relay 5 pin

Changeover_relay.jpg

12v 20A/30A relay
12v 30A/40A relay

24v 10A/20A automotive relay

30 Supply Input
87
Supply Output when relay off.
87a
Supply Output when relay on.
85
Coil ground or negative.
86
Coil trigger or positive from switch.

A control circuit wired to pins 85 & 86 eg, with light duty control switch and wiring , may be used to relay switching of a second circuit with heavier current wired to pins 30 and 87 when control circuit is OFF , changing to pins 30 and 87a when
control circuit is ON

Flasher Relay

flasher_relay.jpg

SAFU003  direction indicator relaySAFU005  flasher relay 4 pin with C terminal for trailer lights warning lamp

31 Ground or Negative
49
Supply Input battery +ve
49a
Supply output to column switch then to indicator lamps.
49b
Second output to direction indicator lamps
49c
Third output to direction indicator lamps

The flasher relay or direction indicator relay pulses power to indicator lamps causing to flash on and off at between 60 and 120 flashes per minute in normal operation.

Always check pin position configuration of relay is correct before fitting

Fuel Pump Relay
1 Ignition Coil (negative pulse)
15
Ignition supply from ignition switch
31
Ground or negative
50
Starter motor cranking signal
85
ground for coil may be switched via engine computer.
30
Battery +ve Supply
87
+ve Supply output to fuel pump.
Wiring terminal designation may be vehicle specific, consult manufacturers specification.

The fuel pump relay may supply power to the fuel pump for a couple of seconds to prime fuel system then shuts off until control circuit via engine control computer grounds coil of relay to switch on again if engine rotation signal is present from crankshaft position sensor or distributor pickup.
Fuel pump relays are vehicle specific in application.

Glow plug controller relay

(L) dashboard preheat warning lamp
(85) or (31)
coil negative
(86) or (15)
from ignition switch , coil trigger +ve.
(30) Battery B+ +ve supply
(87)
+ve output to energise pre heat plugs (glow plugs)

Wiring terminal designation may be vehicle specific, consult manufacturers specification.

The glow plug controller is typically a timer relay which allows diesel glow plugs to heat up for approx 10 seconds to provide pre heating of air in the engine pre combustion chambers to allow easier cold starting. May also have post heat functions.
Operation may also be controlled by engine control unit on later vehicles.

Time delay relay

 

Wiring terminal designation may be vehicle specific, consult manufacturers specification.

Time delay relays may be used for such applications as wash wipe interval, heated rear window,  time delayed motor operation, bus door operation.

 

West Mercia Mechanical Services,
Shrewsbury United Kingdom.
Telephone:
Mobile: 07703 558610

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