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My son's 79' 280zx had HID headlights with projector lenses installed by the previous owner. In the past a headlight would go out and we'd replace the bulb or ballast and it would resolve the issue. 

Recently however the driver's side headlight went out and I can't seem to figure out why.  It's getting power to the ballast  (a little over 12 volts) and we installed both a new bulb and ballast but no luck.


My question however is more in regards to the relay harness.

All over the internet I see where a relay harness is used but in the illustrations they contain only one relay and only one of the factory headlight plugs is connected to trigger the relay. 

In my son's configuration, each headlight has it's own relay and both factory headlight plugs are connected.

Has anyone seen this type setup before? 


I'm thinking I may have a bad ground somewhere, but I'm not sure where the second ground would be.


Thank you.

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That is a strange design ive never seen that before myself with 2 harnesses. Did you try swapping the ballasts side to side? You mentioned there is 12v to the headlight plug, did you use the ground in the plug to test voltage? ground to the frame? or test with a regular bulb? If you know the car side electrical is ok, then you should test your new ballast and bulb on the side you know works. If it works, your other HID relay harness is broken.

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Thanks Evlevo.

I think the problem probably is in the non-working relay harness, but to answer your questions.

  • I checked the car side electrical by plugging a halogen bulb and lens into the factory plug (bypassing the relay harness and ballast on that side) and the headlight worked.
  • Also checked the voltage coming out of the relay itself (where it plugs into the ballast) on the non-working side with a multi-meter and that's where I saw I was getting the 12v going into the ballast.
  • Replaced the bulb itself with a new one and then also checked it with a second new one and neither worked. I bought them as a pair. Just for sanity I'll take the working bulb out and try it in case of the rare event that I received two bad bulbs. I've put that off because the working one is a PITA behind the radiator overflow bottle.
  • The ballast itself on the non working side is a new one. I did swap the new ballast with the ballast on the working side, and the headlight continued to work okay.  I also did that with the relay itself.

I appreciate your reply. This definitely isn't the first thing and won't be the last that is creatively engineered on the car.  The previous owner must have had quite an imagination. A few weeks ago I had to switch the tail light sockets because the turn signal lens would illuminate when you stepped on the brake.  Things that make me blabber in the night.  

Thanks again.

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  • 4 weeks later...

I used to use the HID ones found at Motor Sport but they were not that bright nor reliable.  I have since upgraded to the Vision X 7" round LED headlights and those are the best headlight in my opinion.  They are super bright, have the round halo ring built in and I recommend to get their optional relay so that all five elements can be on when in high beam mode.




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Thanks primaz.


I debated the LEDs but surrendered and restored it all back to the sealed beams. I had a secondary issue with the higher voltage HIDs that I hadn't mentioned before. Whenever I would turn the headlights on and the ignition was on, I'd get a humming out of the alarm system siren speaker.  I tried ferrite coils and some other things to eliminate the problem, but nothing seemed to work.

So it's back to old school for us.

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