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Headlight Retrofit ProjectDR

Discussion in 'LEDs and Optoelectronics' started by Roman2179, Apr 3, 2014.

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  1. Roman2179


    Apr 3, 2014
    Headlight Retrofit Project

    Hello, everybody! I am new to the forums but I figure this is the best place to get some ideas for a project I am considering. A little background information about me, I recently graduated from college. I started out as electrical engineering but finished as IT/Comp Sci. I am very hands for learning new things so difficulty isn't too much of a factor.

    With the introduction out of the way, as the title states, I would like to retrofit HID headlights to my car instead of the halogen lights I have now. The car in question is a 2014 Jeep Grand Cherokee which has the option for halogen lights and HID lights. I would like to make the HID version of the lights behave the same as they would from the factory, hence I have a few questions.

    On the halogen lights, the daytime running lights(DRL) just run the main headlight bulb at about 6 volts instead of 12. The HID lights have a horseshoe LED shape around the light. So the first issue is getting the DRLs to behave correctly. I basically need to set up a circuit where I can trigger two different relays based on what voltage the headlight bulb is seeing. If the line is 6ish volts then I would need to have the LED lights on. When the voltage hits 12 volts, I need it to turn on both the HID bulb and the LED lights, while slightly dimming the LEDs.

    To do this could I use a comparator chip? Is that the only option?

    The next issue is the pass to flash feature because I need to trigger two relays. The HID light are bi-xenon projectors so the brights and normal lights are in a single projector. When the brights are triggered, a shutter in the projector is moved out of the way in order to raise the beam. This is not an issue when the headlights are on but would be an issue when they aren't on. So whenever the high beams go hot I would need the HID bulbs go on and trigger the shutter at the same time.

    I would also need to have PWM LED drivers for the DRLs and turn signals. I would like to stay away from controllers like arduino to do this. Eventually, I would like to design and print a custom PCB with all of these components.

    Sorry about the wall of text for the first post. I will add more details later but it's hard to type it all on the iPad.

    Thanks in advance!

    Last edited: Apr 3, 2014
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    Hi Roman and welcome to the Electronics Point forums :)

    I would like to try to help, but I don't have much experience with car electrics and the terminology you've used.

    There may be others on the forum who have more relevant experience. Also, there have been a number of threads on related subjects before - do a search on DRL to find them. I remember participating in one of them, and we discovered that the lower voltage was not actually a steady voltage; it was a pulse stream.

    So let me try to understand you. You want to replace the halogen headlights on your 2014 Jeep Grand Cherokee with HID - high-intensity discharge - lamps (

    Incandescent headlights have two filaments - dip and full beam. Do these correspond to normal and "brights" in your description? And your Jeep is currently set up to drive dual-filament lamps, so it will have two connection points, one for each filament?

    So you have, or are going to buy, some HID headlamps, and you want to be able to control them from the control signals and power supply that are presently available inside the headlight fixture, right?

    I don't really understand DRL. The control signal from the car is either a steady 6V voltage, or a pulse train, which measures about 6V with a multimeter, and with the existing headlights, this runs the full beam headlight at reduced brightness, right? And this signal is present during daytime when the headlights aren't actually turned on, right? And for the new headlights, you want it to enable a bank of LEDs in a horseshoe shape around the main headlight, right? When the DRL signal is present, you want to illuminate these LEDs at full brightness, but when the connection that can carry the DRL signal has a steady 12V on it, you want to enable the headlight, but also run the LEDs at reduced power? Is that just to get a bit of extra light? Or because it looks cool? Is it legal to do that?

    The DRL signal comes to the headlight on the normal beam connection, right? Or is it the full beam connection?

    Clearly, we'll need to know about the connections to the new headlights. You say there's only a single "projector" for both dipped and full beam, and there's a shutter that moves mechanically to enable high beam. So there will be a connection for the lamp, and a connection to control the shutter. And there will be a connection

    The "pass to flash" feature, is that a spring-loaded control lever that you flick to flash the headlight briefly on high beam as a signal to other drivers? Do you know how this is handled at the moment with your dual-filament headlamps?

    You also casually dropped in a mention of turn signals! Are these part of the headlamp assembly? So these are LEDs in the new headlamps? Are they LEDs in the old headlamps as well? Why do you say you need a PWM controller for them? As far as I can tell from your description, the only LEDs that need to operate at more than one brightness level are the DRL LEDs in the horseshoe shape.

    How much power do the new HID headlamps draw? Do you have a wattage figure?

    I pretty much need to have a pin-by-pin description of the existing signals coming from the car to the existing headlamps, and a pin-by-pin description of the connections to the new headlights. Then we can draw up a table that maps one to the other, then we can design the actual circuit.

    Can you point me to any documentation on the existing headlamps and the new lamps?

    I hope you don't mind answering these basic questions. Unless someone else wants to jump in at this point, I will try to make sense of it all, then I will try to write up a thorough but concise definition of all of the signals involved, as well as a mapping table.
  3. Roman2179


    Apr 3, 2014
    I am bringing this thread back from the dead. I got extremely busy with travel for work and just have not had any time to come back and provide more detail. Now that I have a little bit more time, I will describe in more detail of I am trying to accomplish.

    First off, here is a picture of my current headlight:
    So a few points about this headlight:
    • The main low beam is halogen light bulb housed inside of the projector.
    • The Daytime Running Light(DRL) runs the low beam headlight at about 6 volts.
    • The high beam is separate from the the low beam. (left of the projector in this picture)
    • The turn signal is on the left. When the turn signal is on while the DRL is on, the DRL turns off.
    • The corner light (light behind the orange reflector) is on whenever the headlights are on. This is simple as it has its own wire and behave the same for both types of headlights.
    This is the headlight that I want to install:

    Some points about this headlight:
    • The DRL on this light is the U-shaped ring of LEDs. It runs at full brightness during the day but dims when the headlights turn on at night.
    • The low beam and high beams share the same projector. There is a single High Intensity Discharge(HID) light bulb in the projector. Along with that, there is a shutter that blocks some of the light when the low beam is on. When the high beam is turned on, the shutter is moved out of the way.
    • The turn signal is is the smaller U-shaped ring of LEDs to the right of the projector.
    • The corner lamp functions the same way on both lamps.
    Now that we have the basic information out of the way, I can provide details about some of the issues in the conversion. I will start by saying that there are conversion harness but you lose some functionality. I would like to do this conversion but I don't want to lose features. I essentially want this to behave as close to factory as possible. The main feature that is being lost is being able to turn the DRLs on or off. Currently, I have an option in the car to turn them off. Most conversion harnesses just have you set the option in the car to "OFF" and just run the DRL LEDs at all times.

    The problem lies in the fact that on the top headlights, the DRL and high beams are controlled by a single wire.
    • 0v - off
    • 6v - DRL is on
    • 12v - headlight is on
    I need to mimic this behavior on the other headlight.
    • 0v - off
    • 6v - LED DRL ring on at full brightness
    • 12v - LED DRL ring dims to about half brightness, HID light turns on.
    Essentially, the DRL LED ring is going to be based off of the the low beam headlight being at 0v, 6v or 12v. On the same point, the HID light should only be turned on when the signal goes to 12v.

    The next issue is the high beam. The main point about the high beam is that whenever it's triggered, it needs to move the shutter in the projector out of the way and if the HID bulb isn't already on, turn it on momentarily. This way the flash to pass still works. This is not an issue at night when the HID is already turned on for the low beams but it is an issue during the day when only the DRL LED is on. If I just use the high beam wires from the current light, it will move the shutter out of the way but won't make sure that the actual bulb is turned on.

    I will probably want to use LED drivers for the turn signal and DRL. The dimming of the DRL when the lights turn on would be a nice to have but not really required. Would the components required to do this survive an automotive environment? I guess I could put the circuits inside the car and just have the automotive rated relays under the hood.

    I hope that I covered all of the points and explained what I am trying to accomplish in greater detail. I am sorry about the wall of text.

    Please let me know if i missed anything.

    Thank you for your time!

    So is something like an arduino the best bet or can this be done without resorting to using a controller?

    The programmer in me thinks that a controller would be best to be able to account for all of various factors but I'm questioning reliability for something like this.
    Last edited: Jun 17, 2014
  4. Travis Watkins

    Travis Watkins

    Jun 19, 2014
    I did something similar to my xterra, I did a retrofit and used a bi-xenon projector and built my own custom DRL strip. The problem was that the DRL strip was soo bright at night so when my actual driving lights came on I needed to dim the Cree LED DRL strip. So how I did it was use a relay and PWM to turn them on and off when my driving lights came on. The relay was turned on when the driving lights were turned on so then the PWN turned on... thus dimming the overly bright DRL strip. Hope this can help you out

    Here was how it worked.
    [​IMG]Curtesy Deltaphi216

    The strip that looks like a backwards 7 with an arch in it was the one I built, the halos were just aftermarket.
  5. Travis Watkins

    Travis Watkins

    Jun 19, 2014
    Also you may want to check out its all retrofit and this type of stuff, but I'm sure there's a lot of people on here that could help you out as well.
  6. Roman2179


    Apr 3, 2014
    Thanks for the replies! That schematic will definitely be useful.

    Any ideas on what circuit I could use to trigger different functions based on the voltage? Basically the state of the low beam headlight bulb is what controls the DRL as well as the HID bulb.

    • 0v - No DRL, no HID
    • 6v - DRL on, HID off
    • 12v - DRL on but dimmed, HID on
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