1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Question about the DRL/hi beam circuit

Discussion in '100-Series Cruisers' started by FullyLitLED, Jul 3, 2011.

  1. FullyLitLED


    So on the DRL/hi beam circuit on the 100 series, I heard that when the bulb in that spot is acting as a DRL...it is basically working at half power.

    Does that mean that the bulb is operating at 6V rather than 12V when in DRL mode? Or does it have something to do with amperage or some other electrical term? Dumb question but thanks in advance:D
  2. petrotk40

    petrotk40 SILVER Star

    Tulsa, OK
    based on the one elec engr class I took in college, I'm going to say it will still be 12v, just at a lower amperage. I'm sure it's routed through a different circuit with a resistor to cut the amps, but the voltage should still be 12v.

    are you wondering if the reduced amps will kick power your ballasts? or just the angel eyes?
  3. petrotk40

    petrotk40 SILVER Star

    Tulsa, OK
  4. sonk76


    Philadelphia, PA

    Given that Voltage = Current * Resistance (V = IR), then he only way that the current could have decreased with the voltage being constant is if the resistance in the system had changed (e.g., by adding an extra resistor into the circuit.) While possible, it is a bit of a waste of energy to be using electricity to just "heat" the resistor instead of using it for light output. And I'm not aware of variable resistance light-bulps.

    From my naive perusal of the wiring diagram, I had come to believe that when in DRL mode, the two lights were in effect wired in series, and there by the voltage drop across each light would be 6v in this case (which would of course then reduce the current proportionally)--just as the original poster had suggested.

    I could be wrong, but that was my understanding (I was looking at this before to see if I could use the DRL/High-beam signal as an input into a relay that would turn my driving-lights on/off, and but abandoned the approach due to the relative complexity in this wiring.) Happy to be educated otherwise... :cheers:
  5. In my opinion it could be done either way. It just seems more likely (to me) that a consistent 12V source would be kept around the whole vehicle and that the resistance would just be changed (given ohms law), like a dimmer switch. This, however, is based upon not looking at any wiring diagrams so I could be wrong.

    LJ, why dont you just get a multi meter and test it?
    Last edited: Jul 3, 2011
  6. FullyLitLED



    Its just for the angel eyes! There is currently nothing(in terms of bulbs) plugged into my DRL and hi beam socket so I can plug in anything I want into it...in my case the angel eyes for DRL mode, I have the bixenon wiring spliced into the oem hi beam/drl circuit though:D

    Its like circuit analysis class all over again:mad: lol

    I have one, I need to find it though:cheers:

    In another case, I would not mind hooking up my angel eyes to the heated seats or the cig lighter so they can be on whenever the car is on...which method would be better?

    Or what 12V source would you guys use?
  7. hankinid


    SW Idaho
    The DRL relay puts the high beams in series, so they're effectively seeing 6V.

  8. False. They are wired in parallel. There is most likely a resistor somewhere in the circuit that could be below the driver side headlight, in the engine compartment electrical box, or to the left of the steering column under the kick panel. I know that FJs have a resistor in front of the battery. This is where I will start.

    Reference these threads:


  9. be really easy for you guys to figure it out if you had the EWD :D

    LJ, if you're going to wire the CCFLs to turn off when the low beams are on, you can take a signal wire from the low beam harness and use that to trigger a relay. When the relay circuit is open, you can make that feed power from your seat heat you did to the CCFLs and when the headlights turn on and trigger the relay you added, they'll disable the CCFLs.

    If you want to be able to pull up the ebrake and keep the CCFLs off when you turn the ignition on like factory, then you're going to have to do some serious wiring which IMO isnt worth it. You could also put a switch from the seat heat lead to the relay which would turn the CCFLs off completely unless you closed the switch. There are a dozen or more ways to do it but those are some. I was actually looking at the DRL system in my EWD yesterday and there are definitely ways to do what you want just need to spend the time to do it.
  10. oh and the resistor is next to the airbox on the PS fender. At least on the LXs, there was a campaign to dim the DRLs more as they were too bright from factory. Some of you may find another resistor with two wires going back into the DRL relay #3 with a harness that connects to the original wiring and the relay box.

  11. OregonLC

    OregonLC Brown Thunder Roles SILVER Star

    Portland, OR
    Is there any reason why you couldn't just come off where the ECM powers the DRL relay? Just a simple splice into that line to give signal to whatever else you desire, right?
  12. FullyLitLED


    this is brilliant! Lol I need to figure out how to use relays but I will give this a try later on this week! Thanks loud!
  13. Would you happen to know where this wiring harness is or which wires are what? How did you come by the EWD anyway?
  14. you can, that's a +12v signal as well. trying to keep it simple for LJ since he already knows where the wires i was talking about are.
  15. there's a newer model one floating around the interweb but I've got all the paper manuals and the ewd for a 2000 LC. I'll go figure out which wire comes off the main DRL ECU and which it is going into the DRL relay #3 that's by the airbox
  16. there is a Red w/ Yellow stripe wire that comes out of the DRL Main relay that triggers the dimmer relay which then sends power from the battery to the HEAD(LH-UPR) fuse to the LH highbeam then to the RH one and then into the DRL Relay #3 which then goes to ground. Looks like the lights are indeed in series for the DRL. Once there is signal from the combination switch to trigger the HEAD relay, the low beams both get power and there is a signal wire from the HEAD(RH-LWR) that goes to the DRL Relay #3 that triggers both relays inside there and disables the DRLs.

    yeah, it's confusing.

    edit: there's also a signal that goes from the combi switch to the main DRL relay that tells the system to turn off the dimmer relay. Once you put the combi switch to the high position, it'll reactivate the highbeams at full brightness because of that signal wire from the low beam to the DRL#3 relay I mentioned before
    Last edited: Jul 11, 2011
  17. Wow, and I thought getting my head unit wired up without the factory amp was confusing! Thanks for the info. I was under the lights were in parallel because the voltage read 12V in DRL mode...adding to the confusion...
  18. I could be wrong, but that's how it reads and looks.
  19. Thanks for the help Loud, PM sent!

Share This Page