MTEC H7 4500K HID Installation Guide on 2008 ML320 CDI
First off, I'd like to point out that this conversion kit will work on all 2006, 2007 and 2008 MLs, regardless of model number.
The kit is by MTEC which is a Japanese company. Maruta is their full name I think. The kit ships out of Taiwan.
A word about the ordering process. Only get the kit from the eBay member auto-perfect. He always has 1 or 2 of these kits on sale. Here are some of his current auction URLs:
eBay Link One 
eBay Link Two
The kit is priced at $340 US but in the auction you can make an offer instead. I made an offer for $315 which was accepted. Shipping is $35 in the US and $40 international. For Canada, you have to pick the $40 option. Full insurance is available for $5 more which I took. The kit took 2 business days to arrive at my door, plus a $21 customs brokerage fee to FedEx.
Upon ordering the kit and paying, make sure to let him know in the "payment comment" box what color temperature you're looking for. You can get 4500 Kelvin, 6000 and 8000. 4500K is closest to OEM levels. 4500K puts out the MOST lumens and light on the road. 6000K is more of a blue color, but it puts down less light. 8000K is bordering purple, and that actually puts out less light than stock halogens on the road. I always recommend picking a color in the 4000-5000K range.
The ballasts are made in Japan. The bulbs are General Electric, so everything is quality stuff.
When you get the kit, you will get a variety of wires and parts.
To begin with, let's recap conceptually how this kit works. The bulbs go into the headlight modules obviously. However, the xenon bulbs receive power from the ballast. The ballast, in turn receives power from the ML's original H7 bulb connector. Therefore, we first need to prep our bulbs.
You will notice that the bulb has two wire ends each with a far plastic connector. There is also a rubber grommet halfway along those wires. Then the ballast itself has a single, far rubber wire. And finally there's a separate wire inside a black ribbed tube. Here it is:
So, let's prep the bulbs. We need to use the "black ribbed tube" wire in order to connect the ballast to the ML's H7 connector. On one end, this special wire has two terminals with gold prongs attached. On the other is a plastic connector. We need to shove the gold prong end THROUGH the rubber grommet so that it comes out next to the bulb itself. The gold prongs will reside INSIDE the headlight cover.
You will notice that the rubber grommet already has these two holes drilled into it. Since the gold prongs are wide, use a knife to widen these two holes so you can shove them through. It should like this:
Next, we have to actually attach an H7 male connector to those gold prongs. This will plug into the ML's H7 female connector which previously powered the halogen bulbs. MTEC supplies us with two pink connectors. The connector has holes to put the prongs into, see? When you look close, the prongs have a slight "lip" which locks them into position into the connector when you stick them in. So put those in, with the lips facing each other, inwards. You will hear them click if you did it properly.
Here's what your new male connector is supposed to look like. And also, check out the general scheme of connections.
If you've ever worked with the ML's halogen bulbs, you will know that the metal retaining clips are terrible to work with. Furthermore, they will NOT fit ANY aftermarket xenon bulb without modification. Luckily, MTEC supplies us with a new specially-formed clip for each side. It only goes on one way and it will look like this:
OK, now go downstairs to your car and install everything. The ML has these round headlight back covers which you gotta twist off first. You will notice that since we will be running wires THROUGH this, you cannot install the back covers simply. You will have to drill a hole between 23 and 25mm in diameter so that the rubber grommet from the bulb will be your insulation. For now, you can safely run the headlights without the back covers. Headlight condensation in the inner bottom part may happen but there is no danger - it goes away in 2 minutes. I will write up a further piece about the back cover drilling. My equipment is at the cottage, so I haven't done it yet. Be careful not to touch the bulbs with your hands. It's OK if they touch metal or plastic in the process, but try not to knock them up too bad. You have some troubles with the driver's side headlight because it's cramped on that side, but they do fit properly with patience.
You should mount the ballasts somewhere in the engine bay. Don't use anything sticky because these get hot. The ballasts have two mounting holes. In the ML's engine bay you will find about 5 possible "grounding screws". Unscrew those and screw them back in with the ballasts. Here's where I mounted mine:
The halogen projector lens on the ML seems to be decent. Of course the light isn't spread out uniformly like with a true xenon lens, but it's looking good.
It seems my 2007 Toyota Camry SE V6 has a wider beam pattern.
Anyway, in the video you can see that there is no flickering and there are no "bad bulb" errors in the instrument panel.
Click here to see the short video.
Here is another video of the ML's lights igniting in the garage.
Click here to see the short video.
Here is a video of the ML coming up the garage ramp.
Click here to see the short video. 
