My hids work with No relay. Wow

IMO I would run both with a relay. A 35 Watt HID is 35 Watts without taking into account the power consumed by the ballast, also as someone else stated, in the first couple of seconds when the HID are truning on, the amperage draw can be high.

The relay is mostly for protecting the wiring rather than the switch. There are aftermaket switches that can handle the load. Stock wiring of the truck's headlights already has a Relay, so the point of adding another relay is not for protecting the headlight switch, its for protecting the stock wiring.

BTW the issue is not the wattage, its the current. You can produce the same amount of Watts while pulling more Current from the source. For example a bulb with a thinner filament, vs a bulb with a thicker filament.

More current = more friction = more heat.

 

ok, so lots of bad info in this thread. The only thing you need a relay for is the telescoping hi/low type H4 Bulbs. What he has is the H4 bulbs that have a HID bulb for low beam and in the same capsule have a Halogen bulb for high beam. HIDs draw less current at steady state. The stock wiring is well protected with relays and fuses if you were overloading the stock wiring at all the original fuse would blow. It is true that HIDs do draw more current at start up. It takes several thousand volts at very low currents to start them. This translates to high current at the lower 12v supply voltage. This start voltage is only present for a few milliseconds when the bulb first starts up and tapers off rapidly. Most of this start current is provided by the capacitors in the ballast. The stock wiring is more than adequate to handle this. If anyone is interested i can dig up o-scope shots of the current draw from a HID flashlight design I worked on last year.

 

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