2015 C4 Picasso towbar wiring
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  1. #1
    Fellow Frogger!
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    Default 2015 C4 Picasso towbar wiring

    I am currently fitting a towbar to my 2015 C4 Picasso (5 seater). Installing the hardware was fine, but making the correct wiring connections is another thing!

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    I believe the loom I'm looking for is in the left hand side of the boot area. I suspect I need to work upstream of main loom shown in the first attachment (photo taken behind LHR bumper).

    In the good old days you could see the screws etc. which needed to be undone to remove various bits of trim, but these days everything 'clicks' into place. The trick is to know how it 'unclicks'... and then there's the question of which wires to tap into to activate the bypass relay supplied (second attachment).

    I obtained the towbar kit from Towbars Australia in Queensland. They seem very helpful and no doubt can shed some light on my query. Alternatively, someone on the Forum may already have the answer(s) I seek. Chris
    Attached Thumbnails Attached Thumbnails 2015 C4 Picasso towbar wiring-lhr-bumper-lights1.jpg   2015 C4 Picasso towbar wiring-lhr-bumper-lights-2.jpg   2015 C4 Picasso towbar wiring-lhr-bumper-lights-3.jpg  
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  2. #2
    Fellow Frogger!
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    If the load from the light bulbs is small
    i.e. LEDs you don't need relays
    Just tap into the appropriate wire
    Easily found with a multimeter


    Sent from my F1f using aussiefrogs mobile app

  3. #3
    1000+ Posts robmac's Avatar
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    If the load from the light bulbs is small
    i.e. LEDs you don't need relays
    I would think you are running gauntlet / dreaming if you believe every trailer you connect will have led lighting.

    And if a trailer with filament lamps is ever plugged in, you have a good chance of destroying the transistor outputs on the bsi.

    I'd suggest you play it safe and fit some kind of interface between the the vehicle and the trailer plug. Which is also protection against wiring cock ups between the trailer and car socket.

  4. #4
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    What he said, or you'll get into expensive trouble. The wiring in modern cars is a digital bus, with signals to and from the computer as well as a source of 12v power. The computer can detect even a lamp of the wrong wattage, like a LED.

    You might like this approach - AutoSpeed - Towbar Electronics.. I have seen better solid state variations on this, avoiding relays.

    You can buy complete units.
    Last edited by seasink; 5th February 2017 at 05:17 PM.

  5. #5
    1000+ Posts robmac's Avatar
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    The idea of mechanical relays operating at indicator flash rate doesn't appeal.

    Use these devices as a replacement for the Auto speed specified relays :
    https://www.jaycar.com.au/pcb-mount-...y-12v/p/SY4093

    And total load per relay no greater the 2 amps (24 w)
    Last edited by robmac; 5th February 2017 at 06:39 PM.

  6. #6
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    Thanks for your replies,everyone.

    I believe the relay supplied with the towbar ("7 way bypass relay": see pdf attached to my initial post) addresses the issues raised by robmac and seasink.

    The puzzle is to locate the correct wires in the existing loom to trigger each function - especially as the main rear lights are located in the tailgate. Chris

  7. #7
    1000+ Posts robmac's Avatar
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    Note the cable colors at lamp holders and then break open the loom at a convenient place and do the splice.

  8. #8
    Fellow Frogger! Greg's Avatar
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    Hi
    I think you'll find you really need the factory wiring harness, especially if you have reversing sensors and ABS / Skid control.

    You'll find the dealers may sell a local bar, but always the factory harness.

    The factory harness has it own electronics to tell the car that you've plugged in the trailer plug, and turns off the rear sensors, and changes the ABS / Skid control.

    It comes with a 13 pin circular plug which has a micro switch, so it knows when the trailer is connected. I use an adapter to change it over to a flat plug that common in Australia.

    I think Citroen France has 30% off tow bar harnesses at the moment?

    I can give u a price with a Vin #. It will be about half the price here.

    Best regards,

    Greg
    We Have:
    C5 HDI Exclusive 2.7 '09, Pluriel '09, Berlingo 1.6 HDI '10, C4 VTS coupe. C4 Picasso '08, 2CV Charleston '84 Grey, 2CV, '55 Australian delivered. 15/6 H '55, SM '74 BVM, DS21 EFI BVH, DS21 '67 BVH.
    We Had:
    1930C6F, '73 GS1220 wagon X 2, '75 G special, '75 GS panel van, '74 GS Birotor, '82 GSA panel van with factory AC, '85 CX25GTI BVM, 2002 C5 V6, 2006, C5 S2 HDI, '86 BX19GT, '72 DS21 BVM, '55 15/6H, '54 Lt 15,'73 Dyane, '82 Visa Super X, with Chrono Mecs & factory AC, 1972 SM.

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