Headlight wiring question

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funkaholik
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Headlight wiring question

Post by funkaholik »

I am working on headlight wiring upgrades and am a bit stumped. A 3 prong plug (high windshield) goes to each light, and none of the wires appear to be a ground. Look at this picture of wiring diagram: both fog light and front turn signal light have obvious ground, but headlights do not. What am I missing?

Image
Erik Miller
Concord, CA
1970 Datsun SPL311-29945, owned since '95
1967 Mustang, 428, 5 speed
1969 Camaro convertible, 327, auto
1981 VW Rabbit Truck, 1.6 turbo diesel
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Re: Headlight wiring question

Post by Habitat.pat »

The headlight grounds through the dimmer relay. The common terminal is hot. No idea why they designed it that way.

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Re: Headlight wiring question

Post by redroadster »

Likely the ground to the d relay is a large guage wireing
The headlites need to have a ground wire not tieing into other liter elect components so not to draw current from them especially turning them on or at idle , if a small bulb was in them it could blow or the coil fry
Last edited by redroadster on Sun Feb 27, 2022 11:05 am, edited 2 times in total.
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Re: Headlight wiring question

Post by Curtis »

The headlight power grounds through the headlight switch to the frame. 69-70 only do this. I estimate there is about 40 to 50 feet of wiring for two headlights.

http://kendo-usa.org/datsun/datsun_head ... _69_70.pdf
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Re: Headlight wiring question

Post by Curtis »

Schematics, disco here and disco there, but your feet will do a different step. The wiring harness has so many twists and twirls from the schematic.
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Re: Headlight wiring question

Post by funkaholik »

Incredible. Well, I was going to use a double relay kit from Victoria British, but I don't think that these relays can be triggered by a positive signal, only ground.

I may have to just do the relay upgrade in the tech wiki.

I'm obviously no electrical engineer, but WTF? I don't understand how the lights work without a ground going to them. So only + goes into the lights, and the only ground is at the switch? Wow.

Thanks, guys, for the answers. Much appreciated, as always.
Erik Miller
Concord, CA
1970 Datsun SPL311-29945, owned since '95
1967 Mustang, 428, 5 speed
1969 Camaro convertible, 327, auto
1981 VW Rabbit Truck, 1.6 turbo diesel
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Re: Headlight wiring question

Post by Curtis »

The VB harness has been used on 69-70.

It grounds, it's just that the headlights are always hot. Power goes in to the contact that is usually ground and comes out either the high or low filament. Comes from the fuse box, to headlights, then relay, then switch, then ground.
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Re: Headlight wiring question

Post by redroadster »

It( power , current flow ) comes from the ground side ( provided it's Neg ) and is pulled to the positive side .
This is why you always want to disconnect the neg cable when working on a electrical system etc.
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Re: Headlight wiring question

Post by funkaholik »

So, can I use the VB harness as is? Or would I have to rewire it? I searched threads and see some people talking about using it on 69-70, but no actual description of any mods needing to be done.
Erik Miller
Concord, CA
1970 Datsun SPL311-29945, owned since '95
1967 Mustang, 428, 5 speed
1969 Camaro convertible, 327, auto
1981 VW Rabbit Truck, 1.6 turbo diesel
...Oh, and a daily driver.
viewtopic.php?t=19067
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Re: Headlight wiring question

Post by Curtis »

It was used as is. I don't recall quite what they did. I advised somebody on it at one time. Unfortunately they have now passed away.
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Re: Headlight wiring question

Post by Curtis »

I'm looking at the wiring diagram and trying figure out how they did this.
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spl310
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Re: Headlight wiring question

Post by spl310 »

Curtis wrote: Thu Mar 03, 2022 12:30 pm It was used as is. I don't recall quite what they did. I advised somebody on it at one time. Unfortunately they have now passed away.
Was that Charles? I may be able to go look at his car to see how he did it.
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Re: Headlight wiring question

Post by Curtis »

spl310 wrote: Thu Mar 03, 2022 12:59 pm
Curtis wrote: Thu Mar 03, 2022 12:30 pm It was used as is. I don't recall quite what they did. I advised somebody on it at one time. Unfortunately they have now passed away.
Was that Charles? I may be able to go look at his car to see how he did it.
No, a roadster owner in Florida. I figured it out a way to do it. A bit of messing but it will work. One 5 pin relay would be easier but if it fails you might not have any headlights. Either way carry an extra relay with you. You have to plug in to terminals from one stock headlight plug.
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Re: Headlight wiring question

Post by spl310 »

Curtis wrote: Thu Mar 03, 2022 1:44 pm
spl310 wrote: Thu Mar 03, 2022 12:59 pm
Curtis wrote: Thu Mar 03, 2022 12:30 pm It was used as is. I don't recall quite what they did. I advised somebody on it at one time. Unfortunately they have now passed away.
Was that Charles? I may be able to go look at his car to see how he did it.
No, a roadster owner in Florida. I figured it out a way to do it. A bit of messing but it will work. One 5 pin relay would be easier but if it fails you might not have any headlights. Either way carry an extra relay with you. You have to plug in to terminals from one stock headlight plug.
Charles Godwin lived in Florida. I know that he put the Victoria British harness in, and I thought that he said that you helped him with the install. Could be someone else though.
"Wow, a Roadster!" Stuart Little

1967.5 2000
1967.5 2000
1964 1500
1964 1500
1967.5 1600
1968 chassis
2006 Acura MDX
2013 Volkswagen Jetta TDI wagon
1995 F350 Powerstroke!
More...
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funkaholik
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Re: Headlight wiring question

Post by funkaholik »

This just made me think about some future day after I'm gone, and the next owner of my car looking for advice on 311s.

Thanks guys, for your input. It's good to know that it can be made to work. Let me know if you think of specifics. I'm gonna take a good look at how the VB harness is wired.
Erik Miller
Concord, CA
1970 Datsun SPL311-29945, owned since '95
1967 Mustang, 428, 5 speed
1969 Camaro convertible, 327, auto
1981 VW Rabbit Truck, 1.6 turbo diesel
...Oh, and a daily driver.
viewtopic.php?t=19067