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Thread: Tapping into high beams with DRL (daytime running lights)

  1. #1

    Default Tapping into high beams with DRL (daytime running lights)

    Good afternoon everyone,

    I'm in the process of adding additional set of lamps to the front of my vehicle. I live in Canada and we have mandatory daytime running lights, which is great. What is not great is that I can't figure out how to tap into the highbeam to trigger my lights on. I understand how automotive relays work, but the DRL system is currently beyond me. I have a 2011 Nissan XTerra. Are DRL subsystems identical on all vehicles? Any advice how to sort this out?

  2. #2

    Default Re: Tapping into high beams with DRL (daytime running lights)

    What kind of lamps are you looking to add? To use with your low beams? Off road use? When do you plan on using these lights?

  3. #3
    Moderator Alaric Darconville's Avatar
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    Default Re: Tapping into high beams with DRL (daytime running lights)

    I'm not sure why you want to tap in to the DRLs if you're adding lights for nighttime use. It's common to interlock with the high beams so auxiliary high beams can only come on with the high beams, or to ensure the auxiliary low beams turn OFF on high beam usage.

    Why the focus on DRLs?

  4. #4

    Default Re: Tapping into high beams with DRL (daytime running lights)

    No, the DRL circuitry and drive signal isn't universal across all vehicles. If you tap into the high beam circuit for the enable relay on your auxiliary high beams (so called "driving lights") there will be a variety of technical and legal problems, so don't do it. You're kind of backed into a corner unless you relocate the DRL function. It's not required to be on the high beams, that's just how Nissan chose to do it. You could use one of these to get a perfectly legal DRL function from the front turn signals, then "all" you'd have to do is get the high beam DRLs deactivated. "All" in quotes because this will take a Nissan dealer service department to hook up their diagnostic computer and turn the DRL function off, and in Canada you may have trouble finding a Nissan dealer willing to do so. You probably have a better chance if you install the turn signal DRLs first, so you can demonstrate for the service department that they will not be releasing a vehicle without a mandatory safety feature, but they might still say no. If you're close to the USA border, an American dealer would probably give you less flak about it because DRLs are not required equipment in the US.

  5. #5

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Hmm, ok, this may be a bigger can of worms than I expected.

    My intention was to energize an automotive relay to turn on my offroad only lights only when the highbeam is on. This would make things legal in BC. Now when I went to measure the current/voltage at the light socket I discovered all sorts of interesting values, none of which made sense to me. My understanding is that it's because of DRL -- the headlights are always partially under load to enable dim running lights. I'm still hoping that I can tap into things, but perhaps slightly upstream?

    It's starting to sound like that I should completely bypass the OEM lighting setup and do my own switch.

  6. #6

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Yes. Do your own wiring.

  7. #7
    Moderator Alaric Darconville's Avatar
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    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by eart View Post
    Hmm, ok, this may be a bigger can of worms than I expected.

    My intention was to energize an automotive relay to turn on my offroad only lights only when the highbeam is on.
    To do it right, you really need to set it up so that YOU cannot turn on your offroad lights UNLESS the high beams are on. You don't want them coming on any time you use your high beams. You need a latching relay setup so that you must activate the offroad lights manually while the high beams are on, and then will turn them off when you go off of high beam, requiring manual reactivation.

  8. #8

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by Alaric Darconville View Post
    To do it right, you really need to set it up so that YOU cannot turn on your offroad lights UNLESS the high beams are on. You don't want them coming on any time you use your high beams.
    All of that is true.

    You need a latching relay setup so that you must activate the offroad lights manually while the high beams are on, and then will turn them off when you go off of high beam, requiring manual reactivation.
    This is a deluxe way to do it, but not required. It's perfectly legal to have a regular relay and an on/off switch, which if it is left in the on position will have the auxiliary lamps come on and go off with the high beam headlamps. But the switch does have to be there so the driver can turn off the auxiliary lamps independent of the high beams.

    Quote Originally Posted by eart
    the headlights are always partially under load to enable dim running lights.
    I'm not sure what you're trying to say here. The headlamps aren't "under load"; they're not motors. To provide the DRL function they are fed at about half the normal full voltage. Most often these days this is done by pulse width modulation (PWM), rather than other methods such as an external resistor or putting the two lamps in series with each other -- those methods were used in the past.

    Modern vehicles aren't wired the way old cars were. There's probably not going to be an accessible "upstream" point you could tap into. Instead your operation of the controls inside the car tells the onboard computer which lights to activate in what way.

    You do have to tap into your OEM high beam circuit, because it's not legal or safe to have a simple on/off separate wire-up that lets you turn the auxiliary lamps on or off at will, no matter what the status of the headlamps (off, low beam, high beam).

  9. #9
    Moderator Alaric Darconville's Avatar
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    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by -Virgil- View Post
    [Latching relay] is a deluxe way to do it, but not required. It's perfectly legal to have a regular relay and an on/off switch, which if it is left in the on position will have the auxiliary lamps come on and go off with the high beam headlamps. But the switch does have to be there so the driver can turn off the auxiliary lamps independent of the high beams.
    True, making it sort of the "honor system" but it does run a slight risk of accidental activation. (Granted, one should only turn on the factory high beams in conditions appropriate for high beams, but it's good to be on the safe side.)


    it's not legal or safe to have a simple on/off separate wire-up that lets you turn the auxiliary lamps on or off at will, no matter what the status of the headlamps (off, low beam, high beam).
    But that's the "Oklahoma Method"!

  10. #10

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by -Virgil- View Post
    All of that is true.
    You do have to tap into your OEM high beam circuit, because it's not legal or safe to have a simple on/off separate wire-up that lets you turn the auxiliary lamps on or off at will, no matter what the status of the headlamps (off, low beam, high beam).
    That was the plan. Given that the headlights circuit is not a simple on-off circuit, but a PWM one, how do I tell my relay that highbeams are on?

  11. #11
    Moderator Alaric Darconville's Avatar
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    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by eart View Post
    That was the plan. Given that the headlights circuit is not a simple on-off circuit, but a PWM one, how do I tell my relay that highbeams are on?
    A 220pF electrolytic capacitor across terminals 85 and 86-- taking care that you observe the polarity of the capacitor (connect the + to the 86). Also put a diode with the cathode connected to the 86 terminal. This should smooth out the signal so it doesn't chatter.

  12. #12

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by Alaric Darconville View Post
    A 220pF electrolytic capacitor across terminals 85 and 86-- taking care that you observe the polarity of the capacitor (connect the + to the 86). Also put a diode with the cathode connected to the 86 terminal. This should smooth out the signal so it doesn't chatter.
    Is there an off the shelf component that I can purchase? This is now too far above my comfort level and understanding.

    Thanks for the advice Alaric.

  13. #13
    Moderator Alaric Darconville's Avatar
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    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by eart View Post
    Is there an off the shelf component that I can purchase? This is now too far above my comfort level and understanding.
    I did a quick google for "pwm tolerant relay" and got nothing, but maybe there's another way to phrase it. Whatever you find, if it's not Tyco-Bosch, Flosser, Omron, or T&B, it might not be the level of quality you want. If it's Morimoto or PIAA, *definitely* avoid. You might be able to use a hobbyist type relay (for like RC cars or something) to serve the main relay, so it can handle the PWM input and then trigger the lamp relay. It'll introduce a slight actuation delay, but since your main beams are already coming on it's not that urgent a thing.
    Last edited by Alaric Darconville; 09-11-2018 at 02:23 PM.

  14. #14

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Whoah, time-out. Smoothing out the PWM with a capacitor (or any other method) will not address the issue. Not even close. The DRL feed will still be at low voltage, and all the problems will still remain.

    If you don't want to do it the clean way (disable high beam DRLs, move DRL function to another set of lights, then proceed as normal) then you'd be looking for an electrical black box that can tell the difference between the DRL feed power and the high beam feed power, on the same wire, and provide a full-voltage output only when it senses the high beam power, not the DRL power. If you want that off the shelf, you'd have to have someone build it and put it on a shelf for you to take it off from.

  15. #15
    Moderator Alaric Darconville's Avatar
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    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by -Virgil- View Post
    Whoah, time-out. Smoothing out the PWM with a capacitor (or any other method) will not address the issue. Not even close. The DRL feed will still be at low voltage, and all the problems will still remain.

    If you don't want to do it the clean way (disable high beam DRLs, move DRL function to another set of lights, then proceed as normal) then you'd be looking for an electrical black box that can tell the difference between the DRL feed power and the high beam feed power, on the same wire, and provide a full-voltage output only when it senses the high beam power, not the DRL power. If you want that off the shelf, you'd have to have someone build it and put it on a shelf for you to take it off from.
    Oh, right-- he still hasn't addressed the two-function feed.

    I was thinking that the DRL part was taken care of, but the high beam was still a PWM feed-- a way to maximize bulb life or some other nonsense because you really want your high beams to be well fed, not PWMed for "long life". They're not used often enough to need a long life and they really need to be well-fed to burn the envelopes clean.

    Your high beam indicator light on the dashboard somehow got told-- tap in to that (ostensibly simple depending on dashboard construction).
    Last edited by Alaric Darconville; 09-11-2018 at 10:38 PM.

  16. #16

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by Alaric Darconville View Post
    Your high beam indicator light on the dashboard somehow got told-- tap in to that (ostensibly simple depending on dashboard construction).
    I'm investigating that. Supposedly there's a highbeam specific fuse (why?). If that's the case I can add-a-fuse that.

  17. #17
    Moderator Alaric Darconville's Avatar
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    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by eart View Post
    Supposedly there's a highbeam specific fuse (why?).
    So that way you don't lose ALL your lights if the high beam circuit blows its fuse. Similarly, if the low beams blow a fuse, then you still have high beams (since they'll have blown only their fuse). A fuse with the capacity to run both the low and highs together (as many vehicles do run the low beams while highs are on) is a fuse of high enough capacity to increase the risk of fire due to a closed short.

  18. #18

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by Alaric Darconville View Post
    So that way you don't lose ALL your lights if the high beam circuit blows its fuse. Similarly, if the low beams blow a fuse, then you still have high beams (since they'll have blown only their fuse). A fuse with the capacity to run both the low and highs together (as many vehicles do run the low beams while highs are on) is a fuse of high enough capacity to increase the risk of fire due to a closed short.
    Makes sense, thanks for the explanation. Turns out my nissan has 2 fuses for left and right high beams.


    Truly the unknown unknowns are staggering in number and breadth. I knew about add-a-circuit because I've used it before but I didn't have the imagination to assume that one could be used with high beams.. I'm going to do that tonight. Add-a-circuit to relay activator, relay to lights. Nice and clean and no interior modification.

  19. #19

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Carefully make sure that "high beam" fuse is not also in the DRL power path. If the DRLs are on and they go off when you pull that fuse, you're about to do exactly what you asked if you could do and got told no and why not earlier in this thread.

  20. #20

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by -Virgil- View Post
    Carefully make sure that "high beam" fuse is not also in the DRL power path. If the DRLs are on and they go off when you pull that fuse, you're about to do exactly what you asked if you could do and got told no and why not earlier in this thread.
    I wish I saw your post sooner. Also the fact that manual states, that DRL system doesn't come online until the parking brake is released. Turns out that with the DRL engaged the high beam circuit is also energized so that causes the aux lights to go on. The only time the highbeams circuit is off is when headlights are in "on" mode. I'm going to have to do some more digging I guess.

    ...on the other hand high beams fuse disabling low beams/DRL wouldn't make much sense, would it? Anyway, gotta do some more digging.


    edit: this explains it pretty well https://www.thenewx.org/forum/15-how...ights-drl.html
    Last edited by eart; 09-17-2018 at 10:14 AM.

  21. #21

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by -Virgil- View Post
    If you tap into the high beam circuit for the enable relay on your auxiliary high beams (so called "driving lights") there will be a variety of technical and legal problems, so don't do it.
    Went back and re-read your advice from earlier. Technical problems I'm seeing already. What kind of legal problems would you expect with this setup?

  22. #22

    Default Re: Tapping into high beams with DRL (daytime running lights)

    Quote Originally Posted by Alaric Darconville View Post
    But that's the "Oklahoma Method"!
    Hahaha. Here in Texas the way to see if your lights (rear/front/brake/signals) are working is to way to get pulled over for them NOT working. The "Texas Method".

    Since cops here don't seem to care much about lights, I can only assume they're optional.

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