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Headlight Wiring Issue


Buckner99

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1984 Nissan 720 pickup. I bought an aftermarket set of LED Headlights that have both a low and high beam setting. H4 plug and plays, I plugged them into my plugs. Low beams come on, but on the high beam setting in the light. When I flip to my high beams, high beams come on as high beams but low beams shut off.. stock ones would stay on with the highs. Someone told me to wire in a relay on both sides to where all 4 of my headlights will be on the low beam setting when I turn my lights on, and when I flip to my high beams they will all be on the high beam setting. I just don’t know which wires to tap into. Any help would be greatly appreciated. Thank you.

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720s do not use H4 bulbs. To plug and play you would need 4656 bulbs. However you can simply switch the ground and the low beam wires in your 720 headlight plugs. I've done this

 

ba40857173e40a5c7e6b8fdbc6a2806c.jpg

 

This is the difference between 5 3/4" round and rectangular headlamps.

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1 hour ago, datzenmike said:

720s do not use H4 bulbs. To plug and play you would need 4656 bulbs. However you can simply switch the ground and the low beam wires in your 720 headlight plugs. I've done this

 

ba40857173e40a5c7e6b8fdbc6a2806c.jpg

 

This is the difference between 5 3/4" round and rectangular headlamps.

When I do this, my low beams and high beams both come on when I switch to high beams but in my low beam setting my low beams don’t come on..I guess what I meant was that the H4 plug fits the 4656 plug.. the headlight assembly I got was 4”x6” sealed unit led headlight assembly

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What year is your truck? I think after '83 our trucks changed the way the grounding system activates the headlights. I've seen quite a few people change over to a common ground set up. They used a universal kit off the internet to fix this issue

 

 

This is a screenshot from Facebook, credit to Patrick Smith:Screenshot-20201010-133355.png

 

Edited by SLO720
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4 hours ago, SLO720 said:

What year is your truck? I think after '83 our trucks changed the way the grounding system activates the headlights. I've seen quite a few people change over to a common ground set up. They used a universal kit off the internet to fix this issue

 

 

This is a screenshot from Facebook, credit to Patrick Smith:Screenshot-20201010-133355.png

 

So how did he swap them? 

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Where in Washington are you Buckner99?

 

The 720 wiring harness headlight circuit is a weird animal, it will not tolerate a ground after the headlight relay, nothing will work right if a ground is introduced anywhere in the circuit, so unless you make a completely new headlight wiring harness it likely will not work unless you do what Dmike said if the bulbs/LED lights you are using are wired like round headlights, I know this because I have used 720 wiring harnesses in my 520, and all my 521 trucks I have built(5 trucks total), I made little pigtails like the one in the photo below in my 720 with round headlights.  

028.JPG.26ac436f645cb95d4715fbfe66690286.JPG

 

Even the brights indicator light in the dash screws stuff up if a ground is added, that circuit is not supposed to have a ground on the headlight side of the relay, the dash lights can get screwed up the same way, if you add a aftermarket gauge and splice into the dash lights for power you just added a ground and it screws stuff up, same with a nice stereo with a light, if you splice into the dash light system you just added a ground that is not supposed to be there, none of the light systems have a traditional ground, it takes 2 wires to make a dash light/gauge light work and neither are a ground, the headlight circuit has the ground at the headlight relay, the dash light ground is at the dimmer knob on the dash to adjust how bright you want the dash lights/gauge lights.

The 720 harness works fine until you start changing things, the headlight circuit is especially confusing, since I don't know how your lights/LED lights are wired internally I cannot tell you for sure how to wire them, I am sure there is a way unless you are using headlights that the case of the headlight is the ground like the yellow bright lights that Mercedes had, if the case of the bulb is the ground it will likely never work properly with the 720 wiring harness.

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13 minutes ago, wayno said:

Where in Washington are you Buckner99?

 

The 720 wiring harness headlight circuit is a weird animal, it will not tolerate a ground after the headlight relay, nothing will work right if a ground is introduced anywhere in the circuit, so unless you make a completely new headlight wiring harness it likely will not work unless you do what Dmike said if the bulbs/LED lights you are using are wired like round headlights, I know this because I have used 720 wiring harnesses in my 520, and all my 521 trucks I have built(5 trucks total), I made little pigtails like the one in the photo below in my 720 with round headlights.  

028.JPG.26ac436f645cb95d4715fbfe66690286.JPG

 

Even the brights indicator light in the dash screws stuff up if a ground is added, that circuit is not supposed to have a ground on the headlight side of the relay, the dash lights can get screwed up the same way, if you add a aftermarket gauge and splice into the dash lights for power you just added a ground and it screws stuff up, same with a nice stereo with a light, if you splice into the dash light system you just added a ground that is not supposed to be there, none of the light systems have a traditional ground, it takes 2 wires to make a dash light/gauge light work and neither are a ground, the headlight circuit has the ground at the headlight relay, the dash light ground is at the dimmer knob on the dash to adjust how bright you want the dash lights/gauge lights.

The 720 harness works fine until you start changing things, the headlight circuit is especially confusing, since I don't know how your lights/LED lights are wired internally I cannot tell you for sure how to wire them, I am sure there is a way unless you are using headlights that the case of the headlight is the ground like the yellow bright lights that Mercedes had, if the case of the bulb is the ground it will likely never work properly with the 720 wiring harness.

Eastern Washington. Town of Omak/okanogan. The led headlights I got are the 4x6” sealed units led with the H4 pigtail. My 720 plugs plug right in to the headlight. But they don’t work how they’re supposed to is the problem. The lights are supposed to have a low and high beam setting. The low beam. Only the top row and one in the middle are lit up. When on high, the whole 4x6 assembly lights up. Well when I turn my lights on, my low beams are all lit up. When I flip to my high beams, my low beams shut off and my high beams come on, with all the lights in the unit on.. all I want is for my low beams to stay on when my high beams come on, just like my stock ones did. 

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OK, I just went out and started my 720 with round headlights and checked the wires for power in both positions, this is how mine work in my 720, the outside lights have 3 wires, one wire appears to have power all the time when the lights are on, the other two alternate depending on if it is on high beam or low beam, it appears that either it is not made to work that way/the way you want, or your headlights are not wired into the 720 harness properly, I cannot tell you for sure as I only know how mine work, my outside lights change filaments inside the bulb when I change from low beams to high beams, both lights/filaments are not on inside the round outside headlight bulb when the high beams are on.

Electricity is a mystery to me, so when I figure something out I make a way for me to remember, I use the 720 trucks headlight wiring to remember as it is the easiest to access, my 521 wiper motors the wiring is right there to look at on all my builds, and the instrument cluster I have an 8' X 4' wiring diagram on the wall above the computer, I do them individually depending on what I am going to have for idiot lights on that build.

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On 10/10/2020 at 5:30 PM, SLO720 said:

He made his own, but this is one of the many kits you see online:

 

https://www.amazon.com/LIGHTING-Ceramic-Headlight-Harness-Headlamp/dp/B00GNU37QU

This kit won’t work because the wiring on the Nissan 720 is backwards. It’s a switch to ground system so I’d have to move a bunch of wires around, I’m just gonna make my own

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That kit or any of the universal 4 headlight kit should work okay. There is a main power wire to send power to the relay(s). And the relay(s) are triggered to switch by the signal sent by whichever outer headlight plug you plug it into. You just have to figure out how your kit needs to be wired to function properly. Typically these kits have you add ground for each bulb and don't rely on the wonky nissan system other than for a signal of where to send power. 

 

It will probably be cheaper if you make it yourself, just a little more time consuming. Essentially you are achieving the same thing but you can you heavier wire and make a nicer product also 🙂

Edited by SLO720
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On 10/10/2020 at 10:27 AM, SLO720 said:

What year is your truck? I think after '83 our trucks changed the way the grounding system activates the headlights. I've seen quite a few people change over to a common ground set up. They used a universal kit off the internet to fix this issue

 

 

This is a screenshot from Facebook, credit to Patrick Smith:Screenshot-20201010-133355.png

 


 

where can I find this fill post??? Link perhaps?

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