RE: Replace just the one or both?
ive never had a problem with them, and i have "blue" headlights in her truck, the stratus, the mirada, the bmw, the volvo (moms) and the ramcharger...they arent actually blue...the glass is blue, but when you turn them on, if gives you more of a bright white effect than a blue...where as a regular bulb gives you more of a pale yellow effect.
not to mention that i was a state safety inspector for PA (who has a fairly strict state inspection and emission testing program) and never once did i fail anyone for those types of bulbs.
as for how long it would take, shoot them an email..the owner was very easy to work with when he was a vendor.
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