Originally Posted by
Reelax
well ideally, all HID should be run off a relay harness (in pairs) so that the ballasts get power directly from the battery/alternator. this has nothing to do w/ the ballast being digital or mechanical, all-in-one or separated igniter, plug and play, etc. i have had 8+ kits on 2 different cars and installed on more than 5 galants, in all configurations, so i might know a little about this.
HID needs alot of current in a very short burst to ignite. some cars can handle this w/ their stock wiring, some can not (it also depends on the health or robustness of the charging system). often times one side will ignite and the other will not... this is because one ballast will monopolize the available current and starve the other (this starvation is actually very bad for the ballast and will cause premature failure); a relay harness equalizes this draw since both ballasts are now getting power directly from the battery, bypassing the stock wiring (which is only used to activate the relay, a very minimal draw).
so basically, you don't "need" a relay harness, and can probably get away without one, but if your charging system or stock headlight wiring is suspect, you will end up damaging one or both of your ballasts. i have 3 full sets of HID on my car and have an optima blue top and 3 relay harness to go with them.
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