It protects the switches from high currents, namely HID bulbs, they may consume less wattage, ie 35W or so for OEM applications, but they startup with a large amount power.

"When you open a switch that has current going through it there is a spark. The spark damages the contact points of the switch. The size of the spark and the damage caused is proportional to the amount of power going through the switch. The switches will fail sooner than they would otherwise. The relays are designed for high load, and are easily replaceable in the very rare circumstance that they fail. They're made by Bosch, so failure is unlikely."

From: http://www.mahonkin.com/~milktree/headlight-relay-harness/

 

This will tell you everything you need to know:
http://en.wikipedia.org/wiki/Relay

you need the relay to protect the ballast and to isolate it from the rest of the car. HID's require a lot of current at start up, and it could be more then the oem wires can handle. If there is too much draw, it can burn the oem wires. Your car's electrical system will also fluctuate slightly and thats bad for the ballast too. A relay allows you to power your ballast directly from the battery which makes it more stable.

 

My car also have the light on when I turn the key to ON before starting the car. My HID also have this relay and it dim too when the car is starting.

 

My car also have the light on when I turn the key to ON before starting the car. My HID also have this relay and it dim too when the car is starting.

Really??????

The battery voltage drops down when the starter engages....Amazing.

 

Haha, oh the sarcasm.

Some people do some grounding wire upgrades if you really wanna try to fix the problem, you can do the Big 3 upgrade or just get a grounding kit. All which may prevent some dimming from your lights when you start the car, but I don't see how that really matters that much anyways..

 

I would suggest the Big 3.

 

what is big3 n how it get n instaill it?

 

1) Alternator Positive to Battery Positive (optional fuse)

2) Battery Negative to Chassis

3) Chassis to Engine Block


Replacing/adding larger wire to these three critical spots can reduce or rid your electrical system of dimming and voltage drops. Overall, giving your charging system a larger surface area to travel over, will stabilize power and relieve strain on the alternator and battery.

If you have little cash to spend on a High Output (HO) alternator at the moment.. and the thought of even buying a new/better battery is daunting to you, this is a cheap and quick solution for your voltage issues.

Each wire serves its own special purpose, so you need to upgrade/replace all three for maximum potential of this mod. The Alternator Positive to Battery Positive wire is pretty small on a stock electrical system, so quite obviously upgrading that particular wire will increase power flow from the alternator to the battery. In DC power systems, power flows negative to positive. So upgrading the main grounds is just as important as the main power wire is. And lastly, since the alternator is grounded to the engine block, you need a way to transfer that energy back into the system.

 

is the thread title in english? it sounds like gibberish to me

 

Yes, like some of the other posts.....

 

Lol.