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Wiring Fundamentals: Simple On / Off Switched

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Simple On / Off Switched


00:00 - On and off switched outputs are the simplest you will encounter.
00:03 They're used for actuators that only have two states, on or off.
00:07 Wiring these actuators to the ECU will be done one of two ways which is determined by the current requirements of the actuator.
00:14 For low current devices, typically less than one amp, they can be supplied power from our ECU power supply relay.
00:21 Then connected to the ECU output channel which acts as a low side switch to provide the ground connection when the actuator is required to turn on.
00:29 A common example of this is a charcoal canister purge valve.
00:32 The ECU provides a ground connection for this actuator when the engine is at idle and cruise allowing the stored fuel vapour in the charcoal canister to be purged into the inlet manifold and consumed by the engine.
00:43 For high current devices, typically requiring more than one amp, we need to use a relay to actually supply the power and use the ECU output channel to control the switching coil of the relay.
00:54 We will usually supply power to pin 30, the high current input pin of the relay directly from the battery.
01:01 Pin 87, the high current output, is then connected to the actuator via an appropriately sized fuse.
01:07 The other side of the actuator is connected directly to ground.
01:11 We supply pin 86, the switching coil positive of the relay, with power from the same relay that supplies power to our ECU.
01:20 We connect pin 85, the switching coil negative, to the output channel of the ECU.
01:26 The ECU provides a ground connection for the switching coil of the relay which in turn supplies the high current power to the actuator.
01:34 By wiring the power supply to the switching coil to the same relay that supplies power to our ECU, we eliminate the possibility of ECU backfeeding, as discussed in the power supply section.

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