Headlight Upgrade Wiring Question

Headlight Upgrade Wiring Question

    Nov 23, 2018#1

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    Some of you may have seen that I made this headlight upgrade wiring diagram a while ago but due to being super busy I haven’t gotten around to double checking or testing it. I would appreciate it if someone could confirm or correct the interface between the original wiring harness and the new wiring harness as I am not 100% sure that it is correct. My vehicle is not fitted with DRL’s.

    What I want to clarification on is where the factory wires should connect on each relay.

    White with red trace = which pin on which relay?

    Red with white trace = which pin on which relay?

    Solid red = which pin on which relay?

    On my diagram the factory colours are in the following order if you were looking at the open ends of the female connectors where the male prongs of the bulb slot in (oo-err):

    Solid red = left

    Red with white trace = On top / centre

    White with red trace = Right

    With the engine running I get the following voltages at one of the bulb connectors. I’m assuming that the negligibly low voltages are ground:

    Headlights fully off

    White with red trace – 14V

    Red with white trace – 14V

    Solid red – 14V

    Sidelights (North Americans call them parking lights or something?)

    White with red trace – 0.5V

    Red with white trace – 14V

    Solid red – 14V

    Headlights on

    White with red trace – 13.9V

    Red with white trace – 0.26V

    Solid red – 13.5V

    Brights on

    White with red trace – 13.85V

    Red with white trace – 13.45V

    Solid red – 0.28V


      Nov 23, 2018#2

      maybe you can remind us what you are trying to upgrade?

      remember that the Metro/Swift uses a ground switching method from your light switches to complete your high and low beam circuits.

      your circuit diagram seems to supply a constant +12 volt connection to the bulbs, as well as a permanent – ground wire connection to the bulbs.

       are you trying to convert a ground switch setup to use a switched +12v relay setup?

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        Nov 23, 2018#3

        suzukitom wrote: maybe you can remind us what you are trying to upgrade?

        remember that the Metro/Swift uses a ground switching method from your light switches to complete your high and low beam circuits.

        your circuit diagram seems to supply a constant +12 volt connection to the bulbs, as well as a permanent – ground wire connection to the bulbs.

         are you trying to convert a ground switch setup to use a switched +12v relay setup?

        It is to upgrade the headlight wiring so that the headlights run direct from the battery via a pair of relays that are controlled by the factory wiring. It may be wrong because I repositioned the wires on the part marked “original female H4” to reflect their position in the plug on the car but I havn’t moved the corresponding wires on the new circuit shown in the diagram. I don’t know if making this new circuit would or needs to be positively or negatively switched.

        The parts marked “Original female H4” represent the factory bulb connectors and “New male H4” is a new male bulb connector that I want to use to connect the factory circuit and new circuit together doing away with the need to cut the factory wiring.


          Nov 23, 2018#4

          the relays’ primary (low current) – coil wires will need to be tied into the existing light switch and highbeam dimmer selector switch. I think that would be easiest way to preserve the ground switching method of controlling your main lighting. The use of relays will provide the benefit of protecting your existing light gauge wiring from having to handle heavy current.


            Nov 23, 2018#5

            suzukitom wrote: the relays’ primary (low current) – coil wires will need to be tied into the existing light switch and highbeam dimmer selector switch. I think that would be easiest way to preserve the ground switching method of controlling your main lighting. The use of relays will provide the benefit of protecting your existing light gauge wiring from having to handle heavy current.

            I think I see where I have confused myself; I just have the wire colours on my diagram switched around but are otherwise correct. Is there any advantage or preserving the negative switched system in the new wiring?

            So as it stands I believe the following would work:

            High beam

            Original high beam ground wire (solid red) into pin 86 and out of pin 85 onto the original white with red trace wire.

            New wire from battery into pin 30 and new wire out of pin 87 to the high beam pin of the bulb.

            Low beam

            Original low beam ground wire (red with white trace) into pin 86 and out of pin 85 onto original white with red trace wire (so using this as ground for both high an low beam?)

            Parking light

            I’m not sure about this. Surely it is a separate bulb however when I tested the voltages of each switch position the white with red trace wire acted as ground when the parking light was on. With this new system does it just act as ground for all three modes?

            For reference, this is the relay I am using. 

            Edit: Here is another diagram that I just found on my PC. It looks broadly the same just laid out differently and without the connections between new and old. Would this one work?


              Nov 23, 2018#6

              run two fused 12 or 14 ga wires  (separate wires for each relay) to pin 87 and 86. pin 30 is (+) to lights. run the switched (-) wire from car to pin 85 on relay. run one of the wires from the bulb to ground (this I cant verify which one it is)

              now its been changed from a (-) switched factory output to a (+) switched output.

              just double -checked this on the bench. this is the way to add relays to the lighting system.


                Nov 23, 2018#7

                I believe scotswift’s latest diagram is correct if you wish to retain the existing headlight hi and low beam  switches supplying a path to ground for the low power side of the relay coil.

                85 and 86 are the low power primary coil supply contacts.  87 and 30 are the high power contacts which  ‘close’ (complete a circuit) whenever the low power relay coil is energized and ‘open’ when the relay coil is not energised. (ie. headlights off)

                Headlight Upgrade Wiring Question

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                Headlight Upgrade Wiring Question



                good reading here:

                https://www.12voltplanet.co.uk/relay-guide.html


                  Nov 23, 2018#8

                  so 85 (coil) could be connected to BAT +12v source.

                  and 86 (coil trigger) could be connected to your original main low beam light switch trigger wire which supplies a path to ground whenever you turn the light switch on.

                  30 (fixed contact) is connected to the always hot side of fused +12V.

                  87 (moveable contact) is connected to the low beam headlight bulb spade pin.

                  you would use a second relay for your high beams. relay 86 (coil trigger) connects to the dimmer switch wire for high beams and flash-to-pass ground trigger wire.


                    Nov 24, 2018#9

                    suzukitom wrote: so 85 (coil) could be connected to BAT +12v source.

                    and 86 (coil trigger) could be connected to your original main low beam light switch trigger wire which supplies a path to ground whenever you turn the light switch on.

                    30 (fixed contact) is connected to the always hot side of fused +12V.

                    87 (moveable contact) is connected to the low beam headlight bulb spade pin.

                    you would use a second relay for your high beams. relay 86 (coil trigger) connects to the dimmer switch wire for high beams and flash-to-pass ground trigger wire.

                    I believe this tweak is what you mean


                      Nov 24, 2018#10

                      I’ll be at a PC shortly and will suggest some further tweaks to the diagram. the low power relay coil circuit shouldn’t rely on the same 30A fuse protection as the high current side of the relay circuit.


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