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  1. #1
    Join Date
    Oct 2010
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    kent
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    57

    Led L542 rear lights

    Hi does anyone know how to wire the brake wires on the led coffin lights I’ve replaced the original individual lights on my Dax which worked perfectly before, the wires to the old brake lights are now connected to the L542 green and purple cable so I can’t fathom what’s wrong. I can only get indicator and rear lights to work but no brake lights I checked pressure switch continuity and it’s fine, problem is can’t find installation instructions as I bought them on the forum a few years ago from I think guys name was Paul. I’m all set for MOT booked in for Tuesday so if anyone can help who has overcome this problem would be appreciated. cheers.

  2. #2
    Join Date
    May 2004
    Location
    Perth
    Posts
    4,583
    I can't help you with the wiring, but I think it would have been Paul Blore that you got them from. Also known as Fat Boy on here he is also on The Cobra Register https://forum.thecobraregister.com/
    Cheers, Clive

    (If I'm not here, I'm either in my new workshop or on the golf course!)

  3. #3
    Join Date
    Oct 2010
    Location
    kent
    Posts
    57
    Thanks Clive that might help

  4. #4
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    8,532
    I had this when I installed mine -.....all because i put the LEDs in on one side, and left the filament bulbs on the other.
    Its related to the relative change in current and the way you have now upset the circuit volates as a result.

    Solution: Wire in both sides, and you will almost certainly need to change the relay to one that works with LEDs. Plenty of choice available on ebay, just make sure you get one with the same pin-out as your current relay. Then its an easy pull out and replacement push-in fix.

    HTH
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  5. #5
    Join Date
    Aug 2004
    Location
    Christchurch, NZ
    Age
    58
    Posts
    2,291
    Just to be clear:

    1. You installed two new LED light units
    2. The indicators both work
    3. The sidelights both work
    4. Neither of the brake-lights work

    Is that right?
    Cheers

    Myles D-W

  6. #6
    Join Date
    Oct 2010
    Location
    kent
    Posts
    57
    Cheers I’ll try that then all my other lights work perfectly so must be the relay.

  7. #7
    Join Date
    Oct 2010
    Location
    kent
    Posts
    57
    Don’t seem to have a relay connected to the trace wire (green and purple) also the pressure switch wires are white/black and black earth and I presume it should be green/purple. It’s been twenty five years since I wired the lights so must of done it a different way.

  8. #8
    Join Date
    Mar 2006
    Location
    Oxfordshire
    Age
    68
    Posts
    1,633
    LEDs draw very little current, so you shouldn't need a relay. However, unlike traditional bulbs, they will only pass current one way - so it could be that you need to reverse the wires to the brake light LEDs.
    Alan

    CRC Thames Valley Regional Rep
    UK Rep for European Cobra Club (eurocobra.boards.net)
    Dax 427 DeDion - Huddart SBC 383

  9. #9
    Join Date
    Oct 2010
    Location
    kent
    Posts
    57
    How do you mean reverse Alan. I’ve limited car electrical knowledge, at present the trace wire green/purple runs from the lights to under dash to fuse board then it I presume I connected black/white wire to hydraulic pressure switch so what do I reverse?

  10. #10
    Join Date
    Mar 2006
    Location
    Oxfordshire
    Age
    68
    Posts
    1,633
    The standard arrangement on the Dax is the usual combined 21/5w brake/stop bulb with three connections - a red/black lead to the light switch (via the fuse box), a green/purple lead to the hydraulic brake light switch (no relay), and a common black earth lead. So assuming the L542 LED circuit board expects the same connections, it should operate OK. So although my comment about LEDs and current flow is true, as the brake and rear light share an earth connection the wiring can't be reversed.

    I believe the L542 you purchased from Paul was designed by Chris at Spiyda Ltd, and he sells these as either PCB only upgrades or complete units - see here.

    From personal experience Chris is a very helpful guy, so I suggest you contact him via his website contact page.

    One thing you could try is to swap the rear (red/black) and brake (green/purple) light leads over on the L542 and see if the rear lamps illuminate when you press the brake pedal - if so, then you have a fault on the L542 PCB (circuit board). But as there are multiple LEDs and there are two clusters, then this seems pretty unlikely. More likely is a faulty brake light switch (being over the headers they regularly fry!) or a blown fuse. If you have a multimeter or voltmeter, check that you have 12v between the green/purple wire and earth (black wire) when the brake pedal is pressed. If you don't have a meter, you can test this by connecting a 12v bulb to one of your green/purple leads and the other side of the bulb to earth (black leads) - the bulb should then light when the pedal is pressed.

    Hope this helps!
    Alan

    CRC Thames Valley Regional Rep
    UK Rep for European Cobra Club (eurocobra.boards.net)
    Dax 427 DeDion - Huddart SBC 383

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