Whether you need a relay harness for your HID kit or not depends on a variety of aspects. In some instances, the kit is not necessary, while in other scenarios, you must use it to dodge specific issues of concern.

For instance, the harness can help you bypass the factory wiring of your car and get power directly from the battery if you are experiencing low voltage problems, a CANBUS or DRL issue. Moreover, the kit can also help to reduce the warm-up time of your HID headlights.

By tapping power from the car’s battery to the headlight system directly, you make it possible for the HID ballast and the bulbs to function independently. In this case, the relay harness replaces your vehicle’s original wiring system to provide a more consistent and dependable power source.

Why Use A Relay Harness?

Typically, people use a relay harness in aftermarket HID conversion kits. This assists greatly in dodging intricate electronic control systems problems and also allows a higher current rate to get to the bulbs.

A relay harness uses a 30 amperage fuse electoral wire that connects to the positive terminal of the battery directly. This pulls the signal from the headlight connector and allows power to be channeled from the battery.

HID ballasts receive power through two sets of cables. You will also find two distinct ground wire terminals that ought to be attached to the chassis to complete an electrical circuit.

A List of Concerns a Relay Harness Can Fix

A relay harness can help you make the most out of your OEM or aftermarket xenon headlights. Usually, it can also be used to get more light from halogen, incandescent, and other forms of lighting.

It is capable of fixing a range of power issues allied with HID lighting, including low light output, uneven brightness, intermittent on/off, delayed start, and flickering.

Delayed Start

For an HID ballast to ignite it requires a lot of power. This initial demand for power can pose problems for some vehicles, especially those with weak electoral systems that simply cannot provide the required energy.

The factory headlight connectors of most cars cannot deliver the 7-8 amps per bulb that are needed to light HID headlights.

They can only provide enough amperage to light one HID headlight once the switch is turned on. The power consumption of the ballasts reduces to 3.2 amps within the first 20 seconds, and this is when the second HID bulb can turn on.

The delayed start is caused by insufficient power. Using a relay harness that taps power from the battery directly can help resolve this issue. The harness can instantly pick up 30 amps through the batteries from the positive terminal and ignite both ballasts without any delays.


When the HID ballasts are not supplied with enough power because you are using stock headlight connectors, your lights may flicker from time to time. This concern may also be caused by weak ballasts that cannot convert the required power and get the HID system correctly ignited.

A wiring harness can again provide reliable solutions for this problem. It will ensure enough power is supplied to prevent even weak ballasts from causing HID light flickering.

Low Light Output (Dim or Dark Lighting)

Underperforming ballasts can cause a low light output. The lights may seem dimmer or more blue than usual. This often happens when the weak ballast is unable to convert adequate power to light the headlights at a suitable range.

In this case, the HID wiring harness will ensure more power gets to the ballast. This ascertains that the lighting system can operate at pick performance.

Unfortunately, you are not guaranteed that this will address issues arising from having weak ballasts that cannot increase the light output, irrespective of the power input.

Uneven Brightness

Typically, cars don’t have equivalent amounts of power on each headlight. Whether the driver’s side will be brighter than the passenger’s side or the other way around will highly depend on the wiring configuration of a car.

That said, this imbalance may cause issues with lighting performance once a HID conversion kit is installed.

The headlight with lesser resistance to the wiring, connectors, and other sources of power will be the first to light up. This may result in less power going to the second headlight, and this means one bulb will be several times brighter than the other one.

In some instances, the concern is more manageable, and one bulb will power to full brightness faster than the other one.

Using an HID relay harness can again have this problem fixed. The kit will provide the same amount of power to the ballasts, allowing more consistent and even brightness from the two headlights.

Final Words

Some people use a relay harness to ensure their safety when driving at night and also prevent future lighting problems. On the other hand, you must use a wiring harness to successfully install an HID conversion kit in some vehicles.

I highly recommend using a relay harness even if using one is not mandatory. The kit will assist significantly in extending the longevity of your HID system because it has an inline fuse that protects both your lights and car.

Moreover, the wiring harness will help increase the light output by delivering adequate amounts of power to your HID ballasts.