Car headlight wires

Discussion in 'Electricians' Talk' started by John Bunyan, Nov 26, 2022.

  1. John Bunyan

    John Bunyan Active Member

    I'm replacing some halogen bulbs with LED ones. Problem I've got is the bulbs have positive and negative symbols but the headlight unit only has a black wire and a yellow wire so which goes to which please? Thanks
     
  2. Muzungu

    Muzungu Screwfix Select

    DVM set to DC. If you have the probes the wrong way round it will read negative and vice versa.
     
    John Bunyan likes this.
  3. John Bunyan

    John Bunyan Active Member

    UOTE="Muzungu, post: 2062788, member: 177761"]DVM set to DC. If you have the probes the wrong way round it will read negative and vice versa.[/QUOTE]

    I'm sorry that's lost on me. I thought it was simpler than testing
     
  4. John Bunyan

    John Bunyan Active Member

    I've got a multi meter but would need walking through it.
     
  5. Muzungu

    Muzungu Screwfix Select

    So set the DVM to DC or DCV and the range 20. Stick the red probe and black probes in the relevant wires on the car and switch the headlights on. If the reading is positive your red probe is on +, if the reading is negative your red probe is on -.

    This is assuming that you have your red and black probes in the correct sockets in the DVM, they should be colour coded.
     
    John Bunyan likes this.
  6. MGW

    MGW Screwfix Select

    In the old days blue was positive and black negative with negative earth, seem to remember white and red traces showed main and dip, but it changes with non British or Lucas, every firm has their own colours or numbers, Bosch used numbers and 31 is earth.
     
    John Bunyan likes this.
  7. quasar9

    quasar9 Screwfix Select

    I don’t believe LED bulb replacements are legal. LED headlamps are legal as they have self levelling and fixed. From govt website for MOT testers, for conversion of halogen headlamps to either gas discharge or LED

    a car is a class 4 for MOT and the revised ruling came on 19/03/2021


    “ Class 3,4,5 and 7 vehicles
    For class 3,4,5 and 7 vehicles, the defect ‘Light source and lamp not compatible’ only applies to vehicles first used on or after 1 April 1986.

    Should a vehicle be presented for an MOT test with conversions before 1 April 1986 they must not be failed with immediate effect.

    Vehicles presented with converted halogen headlamp units first used on or after 1 April 1986 will continue to be failed.

    Headlamps must comply with all other requirements of the test and headlamp aim.

    The cars and passenger vehicles inspection manual will be updated shortly.”

    that said, bulbs made properly should have diodes in parallel to the LED to prevent reverse polarity.

    You may also fall foul of insurers as this will be classed as a modification from the manufacturers original specification unless you notify them and naturally they will try raise the premiums.

    a bigger problem is these bulbs often have cooling fins outside of the housing, sometimes with a fan can often be tricky to fit as there is no room.
     
    John Bunyan likes this.
  8. Bazza-spark

    Bazza-spark Screwfix Select

    As @quasar9 says, I don't think LED replacements are road legal.
     
  9. Bazza-spark

    Bazza-spark Screwfix Select

  10. The Happy Builder

    The Happy Builder Screwfix Select

    They should be banned, there was an idiot on the motorway the other night with all his car lamps converted to LED, the front lights were dazzling when on dip and the rear number plate lights gave the impression of a vehicle coming the wrong way along the carriageway.

    Meanwhile other drivers are painting there lights with tints virtually obscuring them and others are making their indicators permanently on and fitting blue lights.
     
  11. quasar9

    quasar9 Screwfix Select

    The technical reason for this non approval is the optics. Halogen bulbs are considered point source and the headlight housing, either the conventional reflector with moulded glass front or projector style with plain glass have been designed to project a beam for the appropriate distances (high or low beam) as well as aiming correctly.

    LED bulbs are not point source, usually made up of a array wrapped round a cylinder. This means existing housing designed for halogen can have light spill beyond the designed beam blinding oncoming drivers. The other issue is the H7/6 bulbs were regulated by the power consumed, usually 50/55watts (although newer bulbs can be up to 150% brighter than a standard version). With LED these wattage values mean nothing. In fact an LED consuming 55watts would totally blind the oncoming driver for many minutes endangering all road users.
     
  12. The Happy Builder

    The Happy Builder Screwfix Select

    Over in the USA there’s a vehicle recall for GMC Terrain cars, because their headlights are a danger to other drivers, the repair is sticky back plastic patches on the lenses, though Canada has not done anything about them yet.

    https://www.collisionrepairmag.com/...secures-free-sticker-installation-for-owners/

    Anyway, in amongst all this discussion, my headlamp bulbs have a key way on them and can only be fitted one way.
     
  13. quasar9

    quasar9 Screwfix Select

    Another problem is the headlamps of newer cars with LED are getting narrower and brighter. In the UK the worst are the Teslas with model 3 the worst. Blinding even on a dull day. My own car has projector style headlamps on both high and low beam and not sure what other dirivers think of them.
     
  14. spannerw

    spannerw Screwfix Select

    Yellow positive, black negative.
     
  15. The Happy Builder

    The Happy Builder Screwfix Select

    Now, when I was a lad we just fitted additional spotlights for use on country lanes and left the headlights alone for general use.
     
    John Bunyan likes this.
  16. John Bunyan

    John Bunyan Active Member

    Ah. I wasn't aware of all that. It's not for myself so I'll inform the person who it's for. Many thanks for all the sound advice.
     
  17. John Bunyan

    John Bunyan Active Member

    Eee when I were a lad we had old bangers for bicycles. We were lucky if the brakes worked. I thought those Dynamo lights that pressed against the tyre to power the light was for posh people. Thought it was clever to wedge a lolly stick in the frame to click on the spokes when the wheel went round. Borrowed me old man's shopper once, pulled a wheelie when the traffic lights went green and the front wheel fell off :(
     
  18. The Happy Builder

    The Happy Builder Screwfix Select

    A lad I know had an argument with a copper after he stopped on his bike at traffic lights with dynamo powered lights and the copper tried to give him a ticket for riding without lights.
     
    John Bunyan likes this.
  19. MGW

    MGW Screwfix Select

    Lucas use to do a book on construction and use lighting regulations, but either there have been huge changes or police turn a blind eye.

    However I know you could always buy head lamp bulbs which were illegal on British roads, 75 watt instead of 60 watt etc.
     
    John Bunyan likes this.
  20. John Bunyan

    John Bunyan Active Member

    @The Happy Builder
    lol. Guess he wasn't the happy biker o_O
    Wonder if they still sell them.
     

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