Headlight circuit short | FerrariChat

Headlight circuit short

Discussion in '365 GT4 2+2/400/412' started by miami355, Nov 11, 2018.

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  1. miami355

    miami355 Karting

    Sep 2, 2006
    136
    Miami, FL
    #1 miami355, Nov 11, 2018
    Woke up this morning and the headlights on my 1984 400i were up and lights were on. They were off when I parked it the night before. The headlight switch wouldn't make the lights turn off. Finally pulled relay "M" which controls "outside lighting", and got the headlights to turn off. I marked it with a red arrow below. All works ok with this relay unplugged except of course the marker lights etc controlled by this relay. I swapped relays, same problem, so I know it is not the relay.

    I usually have the car inside, but I left it out last night, and it rained. So maybe a short was hiding and decided to rear its ugly head with help from the rain. Any ideas where I should look and what I should test for? I did have an intermittent left rear tail light and marker light, so that may be a clue. Thanks for any help.
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  2. theunissenguido

    theunissenguido Formula 3
    Owner Silver Subscribed

    Jan 21, 2004
    2,372
    Argent/Brasil
    Full Name:
    Guido
    #2 theunissenguido, Nov 11, 2018
    Send you a conversation,
    Guido
     
  3. raemin

    raemin Formula 3

    Jan 16, 2007
    1,854
    Lyon (FR)
    Full Name:
    R. Emin
    #3 raemin, Nov 12, 2018
    Have you checked the lifting motor connectors (these are 4 pin connectors "hidden" in the wheel archs): these are quite exposed to water and the green cable is connected to the headlight & headlight flashing relays. As a first step, I would try to unplug both connectors.
     
  4. miami355

    miami355 Karting

    Sep 2, 2006
    136
    Miami, FL
    #4 miami355, Nov 12, 2018
    Thanks, that's a great tip. I can reach under the wheel well and access them?
     
  5. Ak Jim

    Ak Jim F1 Veteran
    Owner Rossa Subscribed

    Dec 23, 2007
    8,489
    North Pole AK
    #5 Ak Jim, Nov 13, 2018
    I think you have to take the front grill off m
     
  6. raemin

    raemin Formula 3

    Jan 16, 2007
    1,854
    Lyon (FR)
    Full Name:
    R. Emin
    #6 raemin, Nov 13, 2018
  7. raemin

    raemin Formula 3

    Jan 16, 2007
    1,854
    Lyon (FR)
    Full Name:
    R. Emin
    #7 raemin, Nov 13, 2018
    The bonnet joint is not properly sealing the engine bay, and all the water that flows over the bonnet ends up either on the lifting motor or the connector. You can even see on my car that the rubber joint is a bit to short which makes things even worse. If you plan to waterproof the car, maybe you should seal the connector with dielectric grease (or baby's petroleum jelly, as this is basically the same, albeit much cheaper and in large quantities). Not sure whether this will solve your problem, but these lifting motors are hosting so many gremlins that taking care of these saves us some headaches in the long term.

    I just remember my father who was infuriated at his mechanics in the late 70's when on the same trip the electric window decided to remained wide open after he paid his ticket at the toll (rain was heavy, and he did not know what the ratchet in the glove box was for). When he finally reached us for dinner the left lifting motor decided to stay open and drained the battery.

    The other issue that comes to mind is water from the AC evaporator that can end-up in some unexpected locations. Relay box is quite close, same story for the instrument cluster connector(s). In this case the most simple solution would be to spay some conformal coating over the relay board plus dielectric grease on all these connectors.

    Let us know what you come to: tracking down the cascade of events that makes a car to switch the light-on, on its own is certainly going to be a challenge. These car do have a soul of their own after all.
     

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