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engine fan setup for g4

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Which pin are you calling the 'switch pin' for the relay?

a simplistic relay, you have 2 pins for the coil, and 2 pins for the switch (N.O. = Normally Open)

On the standard Relay's you have numbered markings (I'm using the Narva 68024) but you could also be using Omrom or Bosch or whatever :)

Going off the Narva top 85/86 = coil (watch that some relay's incorporate a diode across the winding, the Positive of the circuit should go to the side the arrow of the diode is pointing to (Cathode or K or Bar)

The switching part of the circuit gets connected to the other side, numbered 30, 87, 87a (if you have 2 of the same number, they are both joined together, this relay has 2x87 terminals)


  30 = +B (or via a fuse to Battery +ve)

  87 = Normally Open (N.O.) which is where you wire your radiator +ve up to

  87a = Normally Closed (N.C.)

So, there are a few options you can do your circuit, depending on how you wish to drive your relay (High or Low side)

High side = ECU -> 85, 86 -> GND

Low Side = +B (+12) -> 85, 86 -> ECU

Load Side

+B -> 30, 87 -> Radiator Fan +ve, Radiator -ve -> GND

As this circuit is 'series in connection', the components can go in any order, just as long as +B is 1 end and GND is the other, the Relay position and Fan position can be interchanged, as can the Relay numbers 30 & 87

On my ECU, I have Fan = AUX 2 & Fan(HS) = AUX 4 (Fan high Speed)

To test if its wired up correctly (without warming up the engine can be done 2 ways :)

1/. change the switching temperature (ON Temp) to below the current ECT temp (not the preferred way)

2/. change the polarity of the output to the other state, mine is set to low (low Side drive)

The polarity allows you to test the output without changing your set point temperature

*BUT* please check that the output of the ECU is driving the coil of the relay, not on the contact, I don't think the output would like being driven to a state that it could be sourcing or sinking excessive current

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^+1 Best explanation I have seen for ages Rod.

Actually there are 3 ways you can test... Rod's ways will all work, and there is nothing wrong with those, or the feature designed to test something for instances JUST like this ;)

Option #3. Use the 'Test On' function on that auxillary (select 'test on' as the function and 'high' or 'low' side as an option.  But there could also be another thing at play here.  If this is a plug in G4, it is very possible it may not be able to high side drive anything that the OEM set up didn't usually.


What G4 unit do you have Robert.



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