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Thread: Specific wiring query number 723...

  1. #1 Specific wiring query number 723... 
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    My cooling fan is mounted in front of the radiator so it blows (rather than sucking) through it. I want to organise two switches for it, one from the dashboard and one from the thermostatic switch mounted on the front face of the cylinder block. I want to re-use the original Ford thermostatic switch, which was working perfectly well before I started messing about.....On dis-assembly,it was wired as follows: A 4 pin plug ..the wires are Black (two, connected together at the other end) a black/red and a black/blue: these were also twisted together. There are two wires going to the fan, one I have labelled "fan live" and one I have labelled "fan return" as with a + feed to fan live and a - to the return, the fan operates blowing through the radiator front to back as it should. As the original setup in the donor car was a twin fan arrangement and I have only one, my belief is that the black/red and black/blue were the feeds from the switch to the two separate fans, and the two blacks connected together were the live feeds from the fan relay to the switch.Therefore, to reconnect I should run the Purple live feed from the new loom and connect to the twin black wires, and the black/red and black/blue should connect together to the fan wire I labelled "fan live". My wire labelled "fan return" would then be connected to Earth. The pair of wires from my by-pass switch on the dash should connect one to the twin black wires (picking up current from the purple live feed from the relay in the loom) and the other one to the wire I labelled "Fan Live", thus by-passing the thermostatic switch. HAVE I GOT IT RIGHT? Also....to prevent a possible short to earth through the thermostatic switch, should I wire a diode into the black/red and black/blue to prevent current flowing back up to the thermostatic switch when the over-ride is switched on?
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  2. #2 Re: Specific wiring query number 723... 
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    The easiest way to wire a radiator fan and include a manual switch is as follows.
    Use a relay which has a fused supply.
    The terminal on the relay that is usually switched live should be permanent live, you can bridge from the fused live terminal.
    The output from the relay goes to the fan, and the fan is earthed with the other fan wire.
    The earth from the relay should go first to the thermostatic switch then to earth.
    A second wire should come from the earth terminal on the relay to the dash switch then to earth.
    So if either the thermostatic switch or the dash switch provides an earth the fan will run.

    If your car had two fans it is likely that one would come on at a lower temperature and the second at a higher temperature. So you should have a choice of two temperatures if you are just using one fan.
    Last edited by scott h; 07-08-2021 at 10:36 PM.
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  3. #3 Re: Specific wiring query number 723... 
    club member Club Member chris_cussen's Avatar
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    Fan.jpg
    Hi Bill
    The DOHC engine had a two stage thermostatic switch as some models had two fans and they came on at different temperatures.

    I would be tempted to join the black/blue and black/red wires on the thermostatic switch together, that is what I did when I had a DOHC engine.

    The black wires go to earth.

    I’ve knocked up a diagram of how I would wire the system. It will come on when either the dashboard switch is on or when the thermostatic switch is on.

    The ? on the diagram is a point of choice for you. You can either connect it directly to the battery, in which case the fan will run after the ignition is turned off, or to the ignition.

    Don’t forget to fit a fuse in the live feeds

    Chris
    Cabrio, Omex 2.0l 170bhp Zetec blacktop, Omex ECU and wiring loom.
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  4. #4 Re: Specific wiring query number 723... 
    club member Club Member Tony Stott's Avatar
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    Thanks for the sketch Chris, another for the file!!!
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  5. #5 Re: Specific wiring query number 723... 
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    If you have two fans and want to go real fancy, then you could try one of these from Mod-wise.

    http://www.clarion-service.co.uk/cs/...e_Cooling.html

    I had this fitted to my TVR Chimaera, Use to drive this in Europe in plus 30C and never experienced any overheating issues. Plus it never required a manual override, and you dictate just what temp each fan comes in at. When you consider that was managing the cooling of a 4L tuned V8 then I think that's impressive.


    Even if you don't buy this it may give you set-up ideas.
    2000 Marlin Cabrio LWB; 2.0 L Burton Pinto in Ford Nightfire Red with Magnolia leather interior.

    http://www.marlinownersclub.com/wppg...&image_id=2349
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  6. #6 Re: Specific wiring query number 723... 
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    Or the two stage radiator fan switch #FANSW9 £16.20 inc vat Catalogue P334 Issue 34 from Car Builder Solutions and probably others.
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