an H1 HID bulb is a VERY TIGHT fit into a ZKW.the bulbs have to go STRAIGHT in.also,the bases of the HID bulbs are thicker than the halogen H1's,so the metal clips that hold the bulbs in in the back have to be bent slightly.you'll have to drill some holes in the back covers of the ZKW's for the bulbs wires as well.i used some old school chrysler
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PCV grommets to help seal it.just be VERY EXTREMELY GENTLE when fitting the bulbs to the housings.i've broken the ceramic posts on the HID H1's just trying to get them in there.
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that was a $140 mistake. my first attempt took me about 20-30 min. just to get the first bulb in.the second was alot easier once you get the "feel" for it.it was a tight fit no matter what kit or bulb manufactuer i've tried from hids4less to "K2" kits.