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I have a situation where I'm doing wiring for the dashboard of a vehicle. For whatever reason, the turn signal/headlight switch on this vehicle outputs a 6 volt signal on the high beam wire when the low beam is on and a 12 volt signal when the high beam is on. The headlights work as they're supposed to, but the high beam indicator led is activated when the low beam is on since 6 volts is enough to activate it. Does anyone have a simple solution to make the indicator only turn on when there is a 12 volt signal and not when it's a 6 volt signal?

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    What kind of vehicle is "this vehicle"
    – cinelli
    Jul 12, 2013 at 1:55
  • That happened to me when I changed the old classic H4 bulb with the LED one. I haven't checked voltage (yet) but it seems that high beam connector gets 6V when low beam is connected to 12V since high beam indicator (which is connected to high beam bulb connector) lights with half power when low beam is turned on.
    – sbrbot
    Jun 13, 2018 at 21:20

5 Answers 5

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I'll expand on one of cinelli's comments - why not fix the cause rather than the symptom? If you've got 6v on the high-beam feed when the switch is set to dip, this suggests to me there is a problem with the switch - and I'd be worried that it might be causing other hidden problems.

For example, if the lamps aren't relayed (as is the case with a lot of older vehicles), you'll have 6v running through the high-beam filaments all the time the lights are on. This won't be enough to light them, but will shorten the life of the bulbs...

Have you tried another switch?

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  • Got my approval +1
    – cinelli
    Jul 23, 2013 at 13:26
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Try putting a 6v2 zener (400mW) diode in series with the indicator LED. The LED takes about 1.5V so nothing under 7.7V should be able to turn it on. The LED current should be small enough to use a low power zener diode. Make sure you get the diode the right way around.

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  • Though your solution may answer the OP's question, the real problem that needs to be solved is why is there 6 volts on a wire that shouldn't be there. We need more info to handle that.
    – Mobius
    Jul 16, 2013 at 11:32
  • @Mobius - That was not asked for in the OP's question. I have simply answered the question that was asked as per the guidance on answering questions. Perhaps the OP should ask another question - 'why do I have 6V etc..." and deal with it there.
    – user3433
    Jul 16, 2013 at 11:59
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If this is a simple logic chip that is detecting it, then you won't need a lot of current to trigger. In that case, just put something like two 1K resistors in series to ground and divide the voltage in half (the old output will now be in between the two resistors).

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The indicator lamp on some vehicles is also illuminated if the resistance in the wiring is not equal to a certain amount. This is usually cause by using an incorrect bulb (even though the bulb will still plug in and work), If one of the connectors is corrodded etc. A little more details on the year make and model of the vehicle would be helpful. Finding and fixing whatever is wrong sounds a lot less of a hassle then soldering a diode in line to "mickey mouse" the fix.

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I had to figure out where the 6V came from so I drew 2 lamps side by side and gave each a ground connection. I provided them both with 12V to establish 2 lamps in paralell. I then misconnected one of the grounds to 12v and realized 6V on the supply side of the lamps. Poor boy got his wires crossed.

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