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Headlight warning light

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  • Headlight warning light

    I recently installed LED headlights on my 1985 GL 300Z-Turbo 5-Speed. (PIAA LED bulbs inside Valeo 6054 H4 housings --- with city lights) They work great! Excellent road coverage and brightness. But, and there's always a but with these things, my dash warning light now comes on indicating a burnt out headlamp. Of course this is because the current draw is far less than a halogen bulb (or sealed beam), and the circuit believes this to be a faulty or burnt out bulb.
    My question is, without trying to get behind my dash cluster and removing the indicator bulb --- which is likely very hard to do, can I simply cut the white with purple trace wire coming from the headlight sensor located in the engine bay? According to my 1985 shop manual, that is the wire going to that particular warning light directly from the sensor.
    Last edited by NewJerseyZ; 08-09-2017, 09:27 PM.

  • #2
    Could put LED Load Resistors to simulate regular headlamps being installed.


    • NewJerseyZ
      NewJerseyZ commented
      Editing a comment
      True enough ... but that pretty much defeats the usage of LEDs --- power wise anyway.
      I've located the headlight sensor and the plug/connector. I'm going to see what happens if I unplug it completely.
      Hopefully this won't activate a perpetual Bitchin' Betty.

  • #3
    Good information. Please update when you get it figured out.
    Been thinking of swapping to LED headlamps in my H4 housings but haven't been sold on them yet.

    84 AE/Shiro #683/Shiro #820/84 Turbo


    • NewJerseyZ
      NewJerseyZ commented
      Editing a comment
      I have an update:
      I located the headlight sensor in the engine compartment ... rather easy just behind the main relay pack attached to the passenger side strut. (It also has the words "Headlight Sensor" posted on it, so I was pretty sure that was it.) Anyway, I first tried to simply unplug the 6-pin socket plug from below; you can either simply reach under it and pull, or you can remove the sensor first by unscrewing a 10mm bolt that secures it in place. I then tried to turn the lights on with the sensor unplugged ... they popped up, but did not light. Not good. So I then pulled back the rubber boot around the plug which exposed 6 colored wires. Yes, one of them was a white with purple trace wire, as described in the shop manual. Since all this particular wire did was run to the warning light bulb on the dash, I took a pair of diagonal wire cutters and snipped it about 1 inch from the socket. (There is no way this wire can short, as the boot around the socket will easily keep it from touching anything, let alone a body ground.) I then reinserted the boot around the socket and plugged it back into the Headlight Sensor. I again tested the headlights and they functioned properly, both high and low beams. And no warning light on the dash lit up. And in case you're wondering, Bitchin' Betty is not affected.

  • #4
    Further Update:
    From examining the shop manual schematics (Headlight Schematic) I studied the Headlight Sensor detail and noticed that the current from each headlamp flows through a coil near a switch of some sort within the sensor. I'm guessing that the switch is activated by the magnetic field generated from those coils --- one for each headlamp. Since LED headlamp bulbs would draw less current than ordinary halogen bulbs, the magnetic fields will be reduced as well. And this lower magnetic field is not enough to move the switches into their proper position so as to cause the dash light to go on. And it goes on by means of the Headlight Sensor providing a ground path for the bulb. That's right --- the +12 Volts is already applied to the bulb, the sensor merely provides a path to ground when one of those magnetic switches mentioned earlier doesn't operate as designed.

    So snipping the wire mentioned earlier (white with purple trace) prevents the dash bulb from ever grounding, regardless of headlamp bulb current. Nothing else is affected.
    Last edited by NewJerseyZ; 08-10-2017, 10:50 PM.


    • #5
      Final Update:
      After installing and using LED bulb headlights, it became all too apparent that the fog lights (using H3 halogen bulbs) are simply too yellow sitting right next to the headlights. So, unless you are willing to change over the fog lamps as well, you likely will not be happy with the result. I went through several different H3 LED bulbs for my model year (1985) only to find that they simply do not fit in the small housing Nissan gives us behind the lens. But I did eventually find one and will do a small write up on how to install them shortly.


      • #6
        Here are the bulbs that work with the fog lights located next to the headlights on 1984-1985 z31s:
        I chose these for 2 reasons --- 1) They are bright; certainly bright (and white) enough to keep up with the H4 LED bulbs in the headlights. 2) They fit. That's right, these are about the only bulbs that are compact enough to work in the fog lamp housings.
        To install them, it's best to first CAREFULLY remove the black rubber sleeve around the 2 lead wires (red and black) --- done by first snipping off the spade ends near the spades and then slowly sliding the sleeve over the wires until fully exposed. Then snip off the female spade coming from the fog light connector plug leaving as much wire as possible on the connector. Keeping your polarities in check, simply solder (or crimp) connectors that will mate to the two polarities in the connector --- I used a small bullet plug to fit into the connector. The bulb's wire gauge is 20 so as to make a good clean strip without removing any wire.
        Last edited by NewJerseyZ; 09-07-2017, 06:51 PM.