This subject keeps coming up more frequently since more people seem to be buying Halo projector headlights. So, hopefully, this post should help those who are about to make a purchase or just bought a pair.
In most cases, the Halo inside the headlight is just an LED(Light Emitting Diode) that requires about 2-3VDC.
In most cases, the Halo/LED does not have a resistor to limit the current and voltage to the LED. This is very bad. If no resistor is installed, you can bet they will burn out very quickly.
Look at it this way, lets say your car requires to be ran at 3000 rpms to be optimal. This can be achieved with a Cruise Control/Governer. If you drive the car at redline/7000rpms all the time, what do you think will happen ?
The engine would probably fail prematurely.
The same thing applies to the LED. The LED typically only requires about 2VDC and 20mA.
Without the resistor, it's like your giving the LED full throttle(12VDC) and it will eventually burn out. The resistor regulates the current and voltage to the LED at a safe operating level.
Check with your headlight manufacturer to see if they have a resistor in the Halo circuit.
Otherwise, install a 300 to 330 ohm resistor rated at 1/2 a watt
for each Halo/LED on the headlight.
Typically, there are 2 Halo/LED per headlight. So, this would require 2 resistors per headlight or a total of 4.
Below is a diagram showing how the resistors should be connected to the Halo/LED.
The Halo/LED can be turned on by connecting them to your Grille Turn sigs, Bumper Turn sigs, Fog Lights or you could make a custom swtich and turn them on from inside the car independently.