Helpful Tech Tips and Tricks

What is the relay wiring harness with load resistors?

The relay wiring harness with load resistors is commonly used with the aftermarket HID kits. Relay’s first and the main function is to provide stable power supply from the power-sours to the Xenon ballasts and bulbs. Relay pulls signal from the vehicle’s electric system, triggering HIDs to get the power directly from the battery, with the help of the wiring harness. Upon startup, HID ballasts draw more current than halogens to ignite the Xenon gas inside of the bulbs, once fired, they draw less than a stock light. The relay provides initial starting of the HID lights with the proper voltage.

Universal relay wiring harness with load resistors

The resistors ‘load’ the vehicle’s electric system and it ‘thinks’ that the halogen bulbs are installed.

The relay wiring harness has the relay harness itself which gets minimal current flow from the vehicle’s factory socket and make the Xenon lights to get the power from the battery with the help of wiring system.

This relay wiring harness has red power wire which should be connected to the battery’s positive terminal.

The 30 Amp fuse is located on this power wire to protect the lighting system. It will cut off the power flow in case of short circuiting.

Built-in wire with the 9006-type connector should be connected to the ballast feed socket which goes with the HID set on the battery side. The relay with its help get the signal for turning on and off the lights.

The relay wiring harness also includes two wires with the relay ballasts feeds. They should be connected to the ballasts inputs that come with the HID bulb to supply lighting system with the power. The shorter wire should be connected to the battery side ballast, the longer one to the opposite ballast.

The relay wiring harness has two separate grounds which should be screwed to the vehicle’s chaises in order to allow electricity to complete a circuit and return to the vehicle's negative battery terminal.

relay harness resistors

Essential part of this relay wiring harness are two load resistors: the built-in resistor and the separate one. The first resistor should be screwed to the metal on the battery side of the vehicle. The separate resistor should be connected to the ballast feed which comes with the HID bulb on the non-battery side and screwed to the bare metal.

The load resistors are electrical components, which provide resistance within a circuit, thus providing ‘load’ on it. HID lights are a characterized with low resistance and high output application. This predetermines, that the vehicle will not send a constant amount of power to the ballasts causing the lights to flicker and making the error light to show on the vehicle’s dashboard. The load resistors also help enable the usage of HID kit in Daytime Running Lights mode providing it the stable power input allowing the lights to operate properly.


The resistors get extremely hot during operation, that is why they should be screwed to the metal far from the parts which can be easily melted.


Here are the most frequently asked questions and issues connected with the work of the HID Xenon kit which may be resolved after installation of the relay harness with load resistors:

Issue: When I installed the bulbs in my headlamps, I noticed a flickering coming from both headlamps.

Reason: Flickering may be caused by aftermarket bulbs drawing less power than the factory ones. If your vehicle senses a different bulb due to less power which is drawn, it will try to ignite the HIDs repeatedly, which will lead to flickering.

The most common case is when the Daytime Running Lights are the same bulbs, which you are upgrading. This mode makes the bulb operate on the lower voltage causing HID bulb to flicker.


Issue: I have the HIDs acting like strobe lights.

Reason: This effect is caused by Pulse Width Modulation used within the circuit to be commonly applied in newer vehicles. You may also experience a buzzing sound from the HID relay harness, in case you have one without resistors.


Issue: I start the motor and within 5 seconds the headlights turn off and will not turn back on.

Reason: You may experience your aftermarket lights shutting off after a couple of seconds due to specific computer system in the vehicle, for instance, different Can Bus systems. The lights may be consistent if your engine is not running. In most cases, you will face this issue with the engine 'ON'.

Can flickering, shutting off or strobing light issue be resolved without relay with load resistors being installed?

The easiest troubleshooting for these issues is upgrading the fuse to 20 Amp. It will the best option for the HID kit since the resistance will be reduced and the amount of power will be increased. The increase is small and it is safe for your electric system.

The other possible reason is an unsecured connection. Make sure that all the connections are clean and dry, check if there are bent pins.

In case, you upgraded the fuse and checked all connections up, but the issue was not resolved, the installation of the relay harness with load resistors may be needed.

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