Why should I use a Relay Harness with my HID kit?

Posted: October 19, 2010 in How to:, Products, Technical
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I get asked this question a lot. I will always answer this question with another question that leads into a conversation. I am going to try get all this information out of my head and onto this page. I’ll try not to bore you with math or super detailed information. I just want to cover the basics, so here we go.

First things first, What is the application? What location are you installing the HIDs? Low Beams? High Beams? Fog lights? Replacing a stock DRL? (Daytime Running Light)

In most cases you can just plug the HID Ballast directly into your car or trucks headlight socket. Depending on how your car or truck is wired and if it is equipped automatic light controls you can get different results. I have heard the idea that the headlights pull power directly through the headlight switch itself. The added initial power consumption of HIDs will then, over time, burn out your switch which is expensive to replace. If your car was manufactured pre-1980 you may need to heed this warning. But if you own a newer car it most likely has a dedicated, fused headlight circuit starting at a relay. This also applies to your High Beams and Fog Lights.

Note before that I stated a “Fused Headlight Circuit“. This is why we offer an HID Relay Harness. What amperage is the fuse rated for your light circuit? 10 Amp? 15 Amp? 20 Amp? Every vehicle manufacturer designs the light circuit around a specified wattage of the bulb being powered. If the HIDs draw more power than that bulb you will most likely blow the fuse that is protecting the circuit. Some guys just throw the next size bigger fuse in and it works, is that safe? NO, not really. Consider that the gauge of the wiring used is calculated for the draw of the Halogen bulb you just replaced and for the original size fuse that kept blowing. IF you choose to just up the size of the fuse you may end up with a melted wiring harness! Or worse yet, an electrical FIRE! Instead you should install an HID  Relay Harness. It uses the cars light socket to click over a relay and this allows power to be pulled directly from the battery via sufficient gauge wire and a proper size fuse for HID Ballasts to operate.

Does your car or truck have automatic lights? Does your car use this circuit as a low voltage DRL? If you answered YES to either of these questions I would recommend using an HID Relay Harness.

The “Auto Lights” feature on cars will turn your lights on as soon as you turn the key to the Ignition Position. When you crank the engine over all accessories including your lights will turn off. After the engine starts and you let the key go back to the Ignition position the lights will come back on. This will cause misfires from the voltage dipping when it cuts out. In most cases the Relay Harness will correct this problem.

The “DRL” poses more than one problem. Depending on the operating voltage of the DRL will depict if you need more than just an HID Relay Harness. If you can test the voltage with a test meter and it shows a voltage of 6.5 Volts or greater you can use just the HID Relay Harness. If the voltage is less than 6.5 Volts you can use one of our DRL_MODULES. The DRL_ MODULE is my best friend when it comes to finding a solution for low voltage issues. It is essentially a power booster. It will take as little as 3 Volts and bump it all the way up to 14 Volts! You can install this between the light socket and the input of the Relay Harness and voilà! Now you have enough voltage to click over your HID Relay Harness. A properly installed  HID Relay Harness will fix most problems before you ever experience them. It’s a small price and adds a little extra install time, but I like a little peace of mind.

Thanks for reading, feel free to leave a comment or ask a question. You can contact me via email directly here too: tech@v-leds.com.


  1. Matt says:

    You mention to use the DRL Module between the stock harness and HID Relay input harness so it will still activate the relay coil. Only problem with this is when you consider that some(most) vehicles use high beams on a low voltage as DRL lights. If you use this module, you essentially turn on your high beams at full voltage as DRLs, nobody wants that. With HIDs you may need a separate light system for DRLs, to be proper.

  2. Rich B says:

    I bought one of your relay harnesses but it was too short for my 2007 Chevy Avalanche to route/tuck the wires efficiently/cleanly. Do you make longer versions?

  3. […] VLEDS Technical Why should I use a Relay Harness with my HID kit? | V-LEDS Technical […]

  4. Thanks for the input Matt. I was not taking the DRL on a high beam circuit into consideration when writing that. I was focused on the low beam application being used as the DRL. The DRL in a lot of cars/trucks brings out issues like this, especially when the car/truck has a dual element bulb like a 9007/H13/H4 etc. that uses the high beam for a DRL.

  5. We have developed a new relay harness that will be available soon that has longer wire lengths for the Battery connection, Ground connection, Input connector, and both Output connectors. This new harness will replace the our existing HID Relay Harness as our standard. I will make a future post when these become available.

  6. Matt says:

    The fix I’m working towards with a HD Headlight Harness I put on my truck (9004 Halogen Bulbs) is to cut the low voltage DRL wire from the stock light wiring and run two wires to the new high beam wiring. This will send the ~6v to the high beams just like before and for DRLs, they don’t need to be ran through separate relays.
    I don’t believe this will work for HIDs though, correct?

  7. HID Ballasts will not turn on with 6 Volts. And depending on the vehicle, rerouting the DRL circuit is not an easy task or an option at all. If you are doing some wiring mods you may try using a relay to interrupt the high beam controller circuit for the HID bulbs. If you control the relay with the parking light circuit you could have HID DRLs that operate as low beams and when you have your lights on the high beam function would work normally.

  8. Matt says:

    I’m not running HIDs, just Halogen/Xenon bulbs with a HD wiring harness. The vehicle I’m talking about is a 98 Dodge Ram, very little computer control, mostly wiring.
    I do see your point though, most newer vehicles are next to impossible to just redo a little bit of wiring as so much is controlled by the computer.
    Btw, nice write-up and I appreciate the quick and informative responses as well.
    Looking forward to more articles here.

  9. luis says:

    hello there.
    im trying to put hid on fog lights
    but my fog lights are my DRL
    would there be a problem if i put the HID RELAY HARNESS ?
    when they full voltage of the fog light goes in?
    thank you

  10. Yes, you should use the relay harness when installing your HID kit in your fogs. This will ensure that they function properly as your DRL and your FOG lights.

  11. bill says:

    I just installed hids on my 2009 dodge charger,when i start the car the lights comes on after about 3 mins the drivers side flickers then goes out the other side stays on.

  12. hussain says:

    Dear James,

    I own chevy avalanche 08 LT GCC spec. with auto lights as default.
    my problem with HID is after few weeks of installation only one side will work and the other is off after few turning on and off both of them will work after few months of doing that the non imediat working side bulb will burn.

    i think it is a common problem since i can see most of chevys truck 08 and up are running with only one side working HID

    took my truck to the dealer and they said a relay could fix it but not sure abot that?!!!!

    had you found a similar problem or came across it ?
    did the relay kit fixed the problem ?

    I hate that problem with some times flickering HID side and turn off and on to get a stedy both side working and i want to fix it

  13. hussain says:

    Will after reading a lot of what people said about the HID for chevy low beam HID I even went ahead to the dealer which confermed the need of arelay kit to make them work correctly since that auto light and the power sent to the bulbs are low they installed me a kit with 40 amps relay and a fuse that takes power directly from the battery and signal of the OEM socket and the ground of the ballset from the car body the results was catstrofic of that relay kit after few hours I noticed that one side is off again few hours later the extra power has damaged my HID ballest and the bulb has dicharged it gas inside the head light
    3 hours of screaming and cursing at the dealership they removed the kit and replace the head housing that the bulb had discharged in
    That beang said

    My experiance with chevy was bad but with my chrysler 300C 06 the relay kit is working perfictly no problems at all for almst six months now but for the 300 I am using it for high beams

  14. Jerry says:

    i had a question…i tried installing some hids(bi-xenon) but as soon as i would turn on the headlights the fuse on the realy would burn out and no light would turn on, either the low or high…whats causing the relay fuse to blow?

  15. Hey Jerry, we would need to know a little more. You need to contact customer support so they can assist you. sales@v-leds.com Thanks!

  16. Davis Chang says:

    Hello V-LEDS:

    I recently bought a HID H4 Kit for my old 1976 RV.
    However, I can’t help notice that it “requires” a 20A fuse for each line, however there is no fuse box line.
    I hope I don’t need a fuse box, but will if it will prevent any long term damage in the future.
    If I do need it, is it safe to say that I should just splice a fuse box into the positive feed of the 3 prongs, besides the general integrated fuse box for the headlights?

    Thanks in advance.


  17. Davis Chang says:

    By the way, my HID H4 Kit is the standard/slim kit with both Ballast and Relay.

    Thanks again.

  18. Jay says:

    Did you ever find a solution for you Avalanche? I am having the same problem.

  19. V-LEDS says:

    Hello Davis, The relay harness should have a 30 amp fuse inline at the battery connector. This will supply the voltage for both HID ballasts.