Additional fan switch wiring?

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Vinny1979
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Additional fan switch wiring?

#1 Post by Vinny1979 » Mon Apr 29, 2019 6:05 pm

Just wondering if anyone has any tips for a manual override switch for my cooling fans?

on the turbo they run off their own loom via the ecu, so thr rad has no thermo switch as per the nasp.

hence my confusion

thanks
1993 Rover 220 GSi Turbo , 2005 MG ZS 180 mk2

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1234dist
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Re: Additional fan switch wiring?

#2 Post by 1234dist » Mon Apr 29, 2019 6:09 pm

You don't really want a manual one, if you can help it.

But all you need to do is tap into the feed wires and add a switch.
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Vinny1979
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Re: Additional fan switch wiring?

#3 Post by Vinny1979 » Mon Apr 29, 2019 6:12 pm

I want the option of putting them on above what they do anyway.

Track days :laughing2

Its a brand new radiator mind, but still
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Re: Additional fan switch wiring?

#4 Post by Johnny 216GSi » Tue Apr 30, 2019 7:39 pm

Vinny1979 wrote:
Mon Apr 29, 2019 6:12 pm
I want the option of putting them on above what they do anyway.

Track days :laughing2

Its a brand new radiator mind, but still
Do it like this:

Image

You need a DPDT (Double-Pole, Double-Throw) switch (sometimes referred to as a double-pole changeover switch), e.g:

Image

...just search on Ebay using the term "DPDT switch" or perhaps you prefer a "DPDT rocker switch" like the picture. The switch needs to have a 10A rating minimum I would say.

The fan is connected to the two centre contacts which are two separate switches inside the DPDT switch, which change over together. With the switch in one position, the centre contacts are connected back to the ECU wiring and the fan works as it would originally. With the switch in the other position, the fan gets +12v and GND (chassis) connected across it, and it will run continuously. Remember a decent fuse (5A or 10A would be about right) *very* close to the battery.

Just make sure you take a note of the colour coding on the wires so the correct ECU wires connect with the correct fan wires in the "operated by ECU" position. And make sure you know which of the two fan wires is positive and which is ground, so you can wire the other end (which is the "run continuously" supply) correctly.

If you do it right, use the correct cable ratings, fuse it, and insulate and wire-loom everything, this is ultra safe as you're literally disconnecting the fan from the ECU and reconnecting it to +12v and GND when the switch is operated.

You could replace the +12v and GND connections with a +12v and GND output from another temperature controller - if you can integrate the sensor somewhere. There are plenty of aftermarket temperature controllers around for kit cars, etc. Finding a place to put the sensor in the coolant waterflow and making it watertight is another matter entirely... You could use the Rover sensor, in which case you could also switch that out of the original circuit and make it "change over" to feeding a new temp controller. But you'd need a triple pole (3 pole) double throw switch, i.e. 3 single pole changeovers in a single switch, to do that. Or just use some automotive relays with changeover contacts and coils all driven from a single switch to do the same thing.
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Re: Additional fan switch wiring?

#5 Post by Vinny1979 » Tue Apr 30, 2019 8:44 pm

Here's my issue

Mine was a nasp and is now a turbo

many years ago I did the conversion, and the loom was obviously not right for the turbo set up, as the nasp had the thermostat in the rad

Now I had to cut two wires from the ecu and rewire the loom for the turbo loom which i fitted,

not sure how your excellent diagram fits in with what I have? :laughing2
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Re: Additional fan switch wiring?

#6 Post by 1234dist » Tue Apr 30, 2019 8:47 pm

Just look for the two wires closest to the fan and tap in there.
Pastor @ Rover Revival NFP Garage
220 Coupe turbo K785OAT
218 VVC Cabriolet R220OVR
220 GTI M-series J777RAL
Mercedes C270 diesel P80CJM
620 SLI P267LOM HONDA
420 GSI Turbo L191CVP

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Re: Additional fan switch wiring?

#7 Post by Vinny1979 » Tue Apr 30, 2019 8:53 pm

I have also fitted slim line fans :laughing2
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Re: Additional fan switch wiring?

#8 Post by Johnny 216GSi » Tue Apr 30, 2019 8:58 pm

1234dist wrote:
Tue Apr 30, 2019 8:47 pm
Just look for the two wires closest to the fan and tap in there.
Exactly. Philosophy is "if it ain't broke, don't fix it" - or "tread softly but carry a big stick." The idea is to not f**k with anything that defies understanding - so just tap into it at the actual wiring at the fan (the two wires that go into the fan plug) and implement the diagram. With the switch in the "original operation" position, the wiring to your fan is effectively exactly how it is now - nothing has changed so it should still work exactly as it does now (assuming it does work how it's meant to at the moment...). Then with the flick of a switch, you're running the fan off 12v directly and the ECU is safely disconnected from the fan. The ECU might still try to start the fan up if it thinks the temp is too hot (or turn if off it if thinks the engine is too cold) but it can sit there trying to do that as often as it likes - the fan wires from the ECU are effectively "going nowhere" with the switch in the "run continuously" position and you have full control.
Last edited by Johnny 216GSi on Tue Apr 30, 2019 9:58 pm, edited 1 time in total.
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Re: Additional fan switch wiring?

#9 Post by Vinny1979 » Tue Apr 30, 2019 9:52 pm

thank you
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Re: Additional fan switch wiring?

#10 Post by ROVER-25X » Wed May 01, 2019 11:50 pm

On my MGF rad it had mounts for two fans, I got an extra one and fitted it on and made progress of
making a separate wiring loom, switch and relay so I could throw it on in traffic etc, shame the other
OEM rads didn't.
The 25X (2001 ROVER 25 1.4 Impression S, fate TBD)
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