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Wiring 2 low beams & 4 high beams


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So im rewiring the entire car, came around to the headlights and did it just like the original schematic.

(or at least i think so..)

Problem then is than there is some leakage voltage over the H4 low/high beam so that the High beam H1 bulb starts to glow slightly.


Now ive tried all kinds of configurations and its a mess any way i try.


I wonder if anyone who have done this could present a sketch?


Currently i have two wires goint in from the bay to be used as + to high & low.

Both bulbs have been earthed in the bay.


I though simply to use two relays so that one wire would be powered and the other isolated.

But as i said, no matter what i tried this wont work as the other bulbs starts to glow/light up also.


Ive spent two nights reconfiguring the wires i all the ways i could think of but im back at square one.


Hope someone have some experience and a sketch would deffo save the day (and my mood hehe)

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Late at night.. lets try to clarify.


Its a 510, but let me mention again that ive redone all wiring, so i will rebuild as whatever way it has to be wired..

I wont (or at least do not have to) use the high beam indicator in the dash.


But, simplified set apart from the specific car I need to know how to wire two H4 bulbs in paralell, where only one bulb shall be used with low beam, but both with high beam.

How to do this without getting "leakage voltage" trough the bulbs which leads to both bulbs lighting up?

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Should have leeft the stock wiring in place and Added a H4 wire harness.The stock wire harness you tell the new Battery powered harness to turn ON using a relay



Now for this leakage. What type of lamp housings you using? Cibie, Hella,Boesch.


I remeber back in the day the older lamp housing they would ground the bulb out to one side and cause the light to come on. As datsun 510s use a switchable gorund sytem. Meaning +12vpower was already to the plug already and they lights would come ON.. They need to be isolated. Try removing the housing fom the car but with the Plug still installed. see it the light shuts off.



But, simplified set apart from the specific car I need to know how to wire two H4 bulbs in paralell, where only one bulb shall be used with low beam, but both with high beam.


IS THIS RIGHT????YOu want both elements in the H4 bulb to be on???? I think this would get too HOT. I dont reccoment this


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When they both light up are they slightly more dim than they should be? I'm thinking that your ground is not getting sufficient contact. I've seen several instances where 2 bulbs or filaments that share a ground path will both illuminate dimly when the ground is bad.

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Yes, i know how the original harness was wired, and that the lamps were ground switched wont mean the big difference (will affect how the relays are wired)

And I meant both head lamps (ie 4in total) will have the high beam wires powered, and for low beam only the two outer lamps with the low beam wire powered.


Problem is that the H4 bulbs, when you have a second H4(or H1) in parallel with the main lamp, and this one has one side always grounded(or powered)

and then set power(or ground) to the low beam wire of the first H4 you will have a circuit from the input side of the low beam trough the high beam wires and as such they will start to light up.

(voltage will be distributed over them as they are in series, but they still will light up. And when set to high beam there will be some light in the low beam also)

(i checked that the lamps do not have any "frame leakage")


I think i will just need a more advanced relay setup, so that when low beam is on the secondary H4 is fully isolated.

that means one more relay and more wires from the relays inside and to the lamps.


Just though maybe someone had done this setup from scratch on some car sometime and could present a schematic :rolleyes:

I`ll have to start drawing it up and I will solve it, just takes more time than getting the know-how from someone :hug:

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Maybe this will help.



Because we live in a world populated with switched ground 510's, forget calling one terminal ground. Lets call it "common".

The common terminal connects to both filaments.


On a 510, power is applied to this terminal, and the headlight relay, and the light switch grounds either the low beam, or the high beam terminal. Then either the high, or the low beam lights up


On a 521, the headlight switch, and relay apply power to either the high beam or the low beam terminal, and the common terminal is grounded. Again, either the high, or the low beam lights up


If you hook either the low beam, or the high beam terminal to power, and then ground the high beam, or the low beam terminal, the common terminal connects the two filaments in series. Then both filaments, or "beams" of the headlight glow dimly

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putting light elements in series will dim them. Means 6 volt drop across each light element. will not be as brite.


Im really confused on what your doing that a H4 harness or a H4 H1 haness cant do.


I would have used a H4 harness (to battery/or starter lug) and you would have 4 lights going when HIGH BEAM is switch. at FULL POWER Done.


the H4 1 set headlamp set up uses 2 relays low and high. for the outer lamps

stock 510 highs the wiring is OK up to 50/55watts.


if you want more power for the HGIGHS youl will get a 2 set. outer and inner lamps

this will be a 3 relay set


low 1 relays outer lamps

high 1 relay outer lamps

1 relays inner lamps

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So i have finished this and it working. :D


I wired two relays, relay 1 is switching + between low and high beam.(controlled by the steering column arm)

(the COMMON of the H4 ref above picture is always grounded)


Relay 2 is "passive" and switches on when high beam is set, this relay then connects ground to the secondary high beams.

This way the high beam bulbs are always fully isolated and there will be no voltage over them when set to low beam.

(low beam is isolated when set to high since the + wire is then open at relay 1)


The problem all along is not how to wire the low/high beam bulbs, but having another bulb in parallel that shall not be lighted.

The problem would be the same with switch positive or negative.


Take note that this is NOT directly applicable to rewiring headlights to the original 510 harness.

This case is/was a full rewiring from scratch, only using the original switches of the 510.


I have a drawing if someones interested, and sorry i just seem to have a really hard time explaining this, just as it took me some time to figure out how to make it work.

Guess there are other solutions but at least I got it working :)


Thanks for all input!

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That looks like it will work.

Youll want the H4 harness.

Im just confussed as it says its a 4 light harness. Most times it will have 3 relays if a 4 light system

1 relay for low(outer light). 1 for the HIGHS (outer light) then 1 relay for the inner high beams.


25$ is a good price either way. Made in China but so is mine and I paid 39$ I think


maybe on relay has 2 set of contacks but I cant tell. your on your own.

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