I've had several people PM to ask how I did this, so I thought I would start a thread to explain - others who have completed this conversion please feel free to add your input!
This is what I recently wrote to an inquisitive member:
I bought a set of JDMs with the stock H4h bulbs still in them. I removed the H4h bulbs and compared the location of the filament on the H4h to the location of the gas pocket on one of my 9006 hid bulbs - good news is they are exactly the same distance away from their respective bases. This means that once installed the beam pattern will not be affected (btw JDMs have much more even light spread and beam cutoff than USDM headlights).
Now the only problem was to figure out how to carve the 9006 base to fit in the H4h opening of the JDMs. After looking at the opening, the stock H4h bulb and my 9006 hid base for some time, I realized that if rotated the hid bulb the right way, I could file off a certain amount of the tabs on the hid 9006 base to properly fit and hold in the JDM H4h opening. I can't get more specific than that without using pictures, but I'm sure that if you wanted to do this (and bought the JDMs and 9006 HIDs) you would be able to figure it out.
Once that is figured out, place a ziploc bag over the hid glass to make sure there will be no finger oils left on it (which would destroy the bulb!), then take a dremmel and carve the base until it has 3 prongs that will hold in the 3 prong openings of your JDMs.
If you have any questions feel free to ask!
This is what I recently wrote to an inquisitive member:
I bought a set of JDMs with the stock H4h bulbs still in them. I removed the H4h bulbs and compared the location of the filament on the H4h to the location of the gas pocket on one of my 9006 hid bulbs - good news is they are exactly the same distance away from their respective bases. This means that once installed the beam pattern will not be affected (btw JDMs have much more even light spread and beam cutoff than USDM headlights).
Now the only problem was to figure out how to carve the 9006 base to fit in the H4h opening of the JDMs. After looking at the opening, the stock H4h bulb and my 9006 hid base for some time, I realized that if rotated the hid bulb the right way, I could file off a certain amount of the tabs on the hid 9006 base to properly fit and hold in the JDM H4h opening. I can't get more specific than that without using pictures, but I'm sure that if you wanted to do this (and bought the JDMs and 9006 HIDs) you would be able to figure it out.
Once that is figured out, place a ziploc bag over the hid glass to make sure there will be no finger oils left on it (which would destroy the bulb!), then take a dremmel and carve the base until it has 3 prongs that will hold in the 3 prong openings of your JDMs.
If you have any questions feel free to ask!