I would recommend getting some projectors asap The headlamp housing for the explorer were designed for halogen output. When using HID there will be light scatter and no sharp cutoff unless you're using projectors. It's possible that HID light will be distracting for other drivers.
The stock wiring harness was designed for halogen bulbs only. So what's the problem when HID only uses 35 or even 55 watts? When you turn on your HID lights, it takes a lot of power to charge up the gases in the bulb. How much? Twice as much. 13.5 (or more depending) Amps rushed in for about 1 second. This kind of inrush WILL take it toll on your headlight switch built into the explorers internals, it might not happen a month or a year from now, but it WILL happen and it's expensive and time consuming to fix.
Further more using HID in stock enclosures may look brighter but with the way HID bulbs are designed the light scatters differently and you are actually REDUCING your night vision. Now im not trying to convince you out of HIDs, im just saying you -really- want to get projectors in there. And cops are starting to crack down on the HID retro-fits. If its aimed properly in a proper enclosure they really dont care but from what I have read HID retrofitting is now ILLEGAL unless if your car came stock with it. So just be careful, fair enough? Again I am not slamming you at all. Further more watch out for those Ebay kits, ive had a couple of friends who went buggy over those 55 buck ebay HID kits and the ballasts were crap, the wiring was crap, and i even had one friend fry his harness and have a electrical wire fire because of it.
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happy trails