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  • Relay Harness to Factory Harness

    Hi again everyone.So, installing the projectors was a nightmare. First, i found out i had the sealed for life headlights (gray rubber remained nearly cold at 270 degrees for 15 minutes), plastic was nearly melting. That's not what this post is about however. The headlight housings have a single connector going to them, which then separates inside into smaller connectors, separate for the low, high, position etc. Here's what it looks like from the top:



    Here's an image of the relay harness plug in for the factory plug:



    Now, the relay i got has the H4 connector and you can clearly see it's different than mine (i forgot to specify H7, but the H7 is different to mine too). Now, since there are two of the connectors on each side (picture 1), my question is, should i follow them and see if they lead to a connector like the one on the second photo (i'm assuming they join together somewhere and go into a single connector), or what should i do?

    On a side note, what are the connectors which came with the plug but aren't connected to anything? I see no use for them:



    Any help is greatly appreciated.

  • #2
    Headlight relay harnesses typically feed off of the original headlight bulb plug, rather than the harness for the complete light itself which you pictured. The correct plug you should feed to the relay may be internal in the headlight, likely close to where the halogen bulb used to be. Usually with H7 lights, the bulb socket wiring is internal. This explains the "extra plug" that you see on your final photo attached to the bulb. The red/black wire with male metal pins will plug into the original H7 socket (pictured below,) then feed out to a 9005/9006 plug. That plug can be used to either power the ballasts directly, or go to a relay harness input.



    They only need a positive signal from the low beam circuit in order to close the relay electrical loop and power on the ballasts. That is why you only have one plug, since it only requires a single source (from one side usually closest to the battery) to turn on.

    It is less intrusive/destructive that you use the relayed harness off of the internal headlight plugs, rather than cutting/splicing any wiring at all, be it on the body harness or headlight harness.

    You can use the H4 harness plug in a pinch, but you would have to figure out which pin wire is the proper one which feeds to the signal for the relay. High and low pin probably both do, but who knows how those generic harnesses are really wired. Plus, you need to cut and modify the plug, etc. Might be more work than it's worth, rather than buying the correct harness instead. Unless you have all the plug ends on hand, you will lose the ability to easily plug/unplug easily if necessary. Well, wire taps could work also, but the oem style plugs are more robust and cleaner imo.

    Plus, since H4 is dual filament, your H4 harness might possibly have some control box that enables the ballasts to receive power when low and high are switched. Those things are much more bound to fail, rather than simple relays. You will not need that function for an H7 headlight. It is really just another failure point.

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    • #3
      Originally posted by Masticator View Post
      Headlight relay harnesses typically feed off of the original headlight bulb plug, rather than the harness for the complete light itself which you pictured. The correct plug you should feed to the relay may be internal in the headlight, likely close to where the halogen bulb used to be. Usually with H7 lights, the bulb socket wiring is internal. This explains the "extra plug" that you see on your final photo attached to the bulb. The red/black wire with male metal pins will plug into the original H7 socket (pictured below,) then feed out to a 9005/9006 plug. That plug can be used to either power the ballasts directly, or go to a relay harness input. They only need a positive signal from the low beam circuit in order to close the relay electrical loop and power on the ballasts. That is why you only have one plug, since it only requires a single source (from one side usually closest to the battery) to turn on. It is less intrusive/destructive that you use the relayed harness off of the internal headlight plugs, rather than cutting/splicing any wiring at all, be it on the body harness or headlight harness. You can use the H4 harness plug in a pinch, but you would have to figure out which pin wire is the proper one which feeds to the signal for the relay. High and low pin probably both do, but who knows how those generic harnesses are really wired. Plus, you need to cut and modify the plug, etc. Might be more work than it's worth, rather than buying the correct harness instead. Unless you have all the plug ends on hand, you will lose the ability to easily plug/unplug easily if necessary. Well, wire taps could work also, but the oem style plugs are more robust and cleaner imo. Plus, since H4 is dual filament, your H4 harness might possibly have some control box that enables the ballasts to receive power when low and high are switched. Those things are much more bound to fail, rather than simple relays. You will not need that function for an H7 headlight. It is really just another failure point.
      Masticator So, from what i got, i only need the signal from one side of the car harness to reach the relay harness, the other one doesn't matter. The H4 connector in the picture has the white line for low beam signal, the blue one for high, and i'm assuming the brown is ground since it wasn't specified anywhere on the instructions. My plan is to cut the 3-pin connector from that, then use the original H7 internal wire from one headlight to connect the main beam wire to the white, the high beam to the blue and just ground the brown. If that's the case, i'll give it a go once i'm done sanding the headlight lens (don't ask, they had grooves in them), will post pics.

      P.S. I still don't get where i can attach the "extra plug" from the bulb. I can't attach it to the ballast since there's already the two connectors from the bulb going to the ballast, as well as the connector from the relay to the ballast. And if i send a signal to the relay directly from the internal wiring like i mentioned, it'll just be extra wiring at that point.

      Edit: the relay does have a controller, it's the one in the picture below. I'll order a simple H7 one, in the mean time i'll make do with this one since i really need the car and stuff from ali arrives here in like a month minimum.
      Last edited by Skipper; December 3rd, 2016, 11:12 PM.

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      • #4
        You might not need to bother with wire for the H4 high beam on the harness. Could probably just terminate it with heat shrink or something. Maybe just test if it functions with only the H4 low beam wire first.

        The diagram below illustrates the "extra plug" intended purpose.

        You can power the ballast directly with the "BALLAST 12V input" plug, or go to the relay like you intend to do. The other wires you mentioned (the red/blue from the bulb) are just for igniting the HID bulb and they go straight to the ballast's matching plugs.




        Just use the "extra plug" on the side close to the harness and plug the red/male wire it into the original halogen bulb plug, rather than cutting the original plug to connect the wire. You could also plug the ground in and use that to attach to the H4 plug ground. Yes, they are extra wires at this point, but it saves the original plug/wires in its full unadulterated state in case a problem arises or you want to change something on the light. Plus, it's already through the grommet so you won't have to feed any wiring yourself.

        edit: I have used that same H4 harness with the controller on my dad's car with those cheesy H4 bixenon bulbs (the glare is really not bad at all because of the "shield") and it (the harness) has failed on me before. I switched it to a Morimoto Moto Control one and it's going strong. It is probably just from prolonged and extended usage. Low beams are on all the time on his car since they double as the drl from the factory. He likes it that way, plus since the HID bulbs are already on, he can flash high beams at full brightness in the daytime.

        Also, since you say you are getting a new harness, you could get away with a 9005/9006 one, assuming that you use the "extra plug" that is on your bulb grommet. It will be easier and also plug and play. The generic/China style harness will have direct H7 plug to the relay input signal, feeding an H7 male plug using the grommet on the bulb will be a challenge.

        If you happen to order the Morimoto harness, all the single filament bulb harnesses are a 9005/9006 harness with an adapter for the particular bulb needed for the application. That is unless they changed something recently that I don't know of yet. Also, if you are interested, I have a used 9005/9006 Morimoto harness that I keep as a spare. PM me if you're interested



        Last edited by Masticator; December 3rd, 2016, 11:53 PM.

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        • #5
          Masticator Hahah thanks, but i don't think the price of shipping to Macedonia would work

          I'll be installing them tomorrow, and here's the plan:
          I considered using the extra wiring from the bulb to connect the existing harness wiring to the ballast directly, but the reason i got the relay was so that i don't have to run power from the standard harness, as the relay draws power straight from the battery. I'll probably connect it the standard way (relay to ballasts), with the exception that i cut off the relay harness input plug at the end, and:
          a) i'll send positive low and high beam wires to the white and blue wires (picture below), ground the remaining brown, and see if the relay works with low beams and if it indeed flips the solenoid when i power the high beams
          b) if that fails i'll only send a positive wire from the low beam to the white wire, and connect the solenoid directly to the high beam stock wiring (so when i switch them on, rather than going through the relay, they just power the solenoid). Again, i'll avoid this method as i'm most comfortable with the relay harness as it draws power from the battery directly.

          Here's what i'm proposing to cut-off (the input for the relay), and connect the positive batteries from the low and high beams:
          Last edited by Skipper; December 4th, 2016, 08:42 PM.

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          • #6
            Any update Skipper ?

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