jbm blog

Mercedes CLK320 / AVIC D3 install

September 24, 2007 – 5:00 pm

Earlier in the year I installed a Dension IceLink in my SL55, and thereby came to experience the joys of integrated ipod playback while driving. The IceLink is imperfect because the integration with the COMAND head unit is limited. My CLK320 is a 1998 edition, and consequently has a pretty poor head unit by modern standards. It has no GPS, no text display and of course no auxiliary input (though it does have a cassette deck!). I therefore decided to replace the whole thing with a new head unit, and chose the AVIC D3

The D3 is a double din unit, while the OEM head unit is single. Mercedes installs a useless storage tray beneath the single DIN OEM unit, so pulling that out exposes a hole big enough to shove the D3 into, after removing the spacer bar. I figured this was easy enough to do, and hence ordered the D3 instead of one of the single DIN units with the pop out screen. I don’t like the way they look, plus I think it would partially cover the dash vents.

The first order of business of course is removing the OEM head unit. Doing this requires a special tool (apologies for the poor quality photos. I couldn’t find my camera so these are all taken with cell phone)

I ordered this from Enfig car stereo.The triangular shaped section worked best, with the wedge part facing inwards.

The storage bin comes out with a little pressure, and you’ll need to move the gear selector out of the way slightly. The head unit carries three connectors plus the antenna. By happy coincidence, the connectors are identical looking to those on the COMAND head unit in my 2004 SL55. Due to the unusual way I installed the Dension IceLink I had a spare male-to-female loom for the 3 connectors which I could modify for use in this project. I cut off the male side and directly soldered the AVIC connectors to the female side. This leaves the loom in the dash untouched - handy if you ever want to go back to the old system. Of course I was fortunate in already owning a set of connectors, but you’ll find these commonly available on eBay.

A frequent problem is locating the VSS signal. I reasoned that even though my car didn’t come with GPS, the signal was present in the loom because:

• A primitive single DIN GPS was available for the car as an option.
• The loom would be the same even without factory installed GPS
• The wiring loom is identical to the 2004 COMAND unit which has GPS, and therefore I assume VSS.

I have a subscription to www.alldatadiy.com covering my SL, which was indispensable for the IceLink install. I added a subscription for the CLK which was equally good. I recommend you get one if you’re thinking of self install.

Planning the install

Reading the wiring info for the OEM head unit, I suspected that the audio coming out was line level, not speaker direct. Of course the AVIC outputs both, so no big problem, but I decided to test this to be certain. I don’t own an oscilloscope so I tested my theory by feeding line out from a cheapo portable CD player into the loom, avoiding risking the AVIC and confirming that the head unit does in fact output line level (therefore there’s a power amp elsewhere in the car. Turns out it’s behind the left panel in the trunk). I decided to keep the power amp because rewiring the speakers direct to the head unit was more trouble than I felt was justified.

I also decided to solder the AVIC loom to the stub female loom I had. I prefer solder joints where possible, and I can make all the joints on the bench, outside the car. Nevertheless I first labeled everything and then made a test setup using screw terminals. Only once this worked did I finally solder.

Planning the mounting

After pulling out the head unit I realised the AVIC would need the Pioneer double-din mounting kit. I guessed the hole I’d get after pulling the storage in and cutting the spacer would be about right so I ordered the kit, and put the car back together and waited a week for it to arrive.

The spacer can be cut out with a small hacksaw (or a regular hacksaw blade without the frame, held with gloves). You’ll also need to remove some plastic material on the sides to get the double-din kit to fit correctly. No big deal.

Wiring from AVIC to Mercedes loom

There are 3 loom connectors, A B and C, from bottom to top. Connector A carries power, control signals and VSS. Connector B carries the 4 audio channels. Connector C carries CAN-Bus and D2B bus control signals (none of which are needed here, so you can ignore it)

The pins on the connectors are numbered as follows, looking into the pins of the plug on the loom with the clip on the right:

A (bottom connector on OEM head unit) Pin#/Wire color (background color then stripe), Loom function
pin 7 Pink/Green 12v switched to AVIC Red	pin 5 Blue/White Pwr Amp control out To AVIC Blue/White	pin 3 Yellow/Black Mute input(a)	pin 1 Green/Purple VSS To AVIC Pink
pin 8 Brown Ground To AVIC Black	pin 6 Gray/Blue Dim level input To AVIC Orng/Wht	pin 4 Red/Blue 12v unswitched To AVIC yellow	pin 2 Ignore

B (middle connector on OEM head unit) Pin#/Wire color (background color then stripe), Loom function, line out on AVIC
pin 7 Left/Rear Audio+	pin 5 Left/Front Audio+	pin 3 Right/Front Audio+	pin 1 Right/Rear Audio+
pin 8 Left/Front Audio-	pin 6 Left/Front Audio-	pin 4 Right/Front Audio-	pin 2 Right/Rear Audio-

At this point I strongly recommend powering up the AVIC and checking all the audio functionality. I then made the parking brake modification per the AVIC411 forum, so I could enter nav data while driving.

I found the OEM head unit uses a slightly different radio antenna connector than the AVIC. This was easily solved by cutting off the stubby little plug and replacing it with a standard one.

Additional wiring

You need to run cables for the ipod, GPS antenna, reverse sensor, backup camera (I ran some coax cable for this even though I don’t have one. I might add it later)

I chose to place the ipod in the center storage bin. It’s certainly easier in the passenger glove box, but that’s too inaccessible for me. It’s worth pointing out that although the AVIC has music nav UI that looks like an ipod, doesn’t work like an ipod. You might still need to get to the ipod, IMHO. Running the cable from the head unit to the center storage requires these steps:

• Remove the ash tray
• Remove the trim around the shift lever (there are no screws. Lift up the edge exposed by the ash tray)
• Remove the cup holder
• Open the center storage bin. Remove the two screws at the front edge.
• Feed the cable from the storage bin, through the cup holder box, past the shifter and behind the ash tray lid, emerging at the head unit.

I decided to tap into the reverse signal in the trunk, rather than try and find it near the gear selector. I’m pretty sure the signal doesn’t come into head unit loom too. I also decided to place the GPS antenna on the trunk lid.

Running cables to the trunk requires these steps:

• Remove the passenger glove box: remove the two ‘rubber’ screws, then 2 top (one behind lamp) and 2 bottom (concealed behind little covers).
• Remove the passenger sill plate.
• Peel back the door seal at the rear of the passenger door opening.
• Pop out the rear passenger right side trim

Pull the cables from the head unit opening, past the glove box opening, tucking them behind the passenger footwell trim before bringing them out at the sill plate. There’s a covered channel beneath the passenger sill plate that eases the task of running cables past the door opening. Open the little covers carefully - the clips break easily.

You can now fold back the rear passenger trim panel and work the cables around the edge of seat cushion, before letting them emerge in the trunk. The trunk trim panels are held with simple clips and can be bent out of the way.

The trunk hinge has a set of clips concealing a channel for cables - perfect for running the GPS antenna. For a scary moment I thought the GPS antenna cable was going to be too short. After pulling the maximum amount through the trim panels I found it was OK, but I only had perhaps 3″ spare.

I tapped into the reverse signal by tracing back the reverse lights. The cable in behind the panel shown in the photo and is Yellow with white stripe.

Before putting back the trim and panels I went for a test drive. Deep disappointment: Alternator whine. I went online and did a bunch of research re ground loops. Here’s what I learned and tried:

• Ground is important, especially getting a single, true ground. I tried a bunch - direct to the battery, direct to the body close by. I joined the other grounds from the other loom (carrying control signals - unused otherwise for AVIC).
• The line out signals are coax as they emerge from the AVIC, but they are twisted pair within the main loom. I initially felt this was the culprit, but I read some very will informed articles that suggested each is electrically identical. Plus of course the OEM unit used the loom, twisted pair and all, with no alternator whine.
• I considered eliminating the power amp. By using the twisted pair line out signals in the loom, and directly connecting them to the speakers (bypassing the power amp) plus of course using the speaker output on the AVIC, I knew I could do this. However the connector on the power amp is pretty intimidating and it would be hard to reverse this modification. so far everything else I’d done could be simply unplugged if the need ever arose.\
• I removed all the extraneous wiring from the AVIC by removing the connectors from the block using a fine screwdriver to pry out the retaining pin.

In the end I decided to try the good old isolating transformer trick, the option of last resort. I bought these from my local radio shack:

Now, I expect someone is going to berate me for the loss of audio quality, especially from Radio Shack. I considered the possibility the quality might degrade, but being the pragmatist I am let me point out:

• The acoustics in a stationary car are dreadful anyway. You can spend what you what on monster cable and fancy speakers, the fact remains that cars are noisy places, even when not moving. Drive it at 50mph and any quality loss will be hidden behind the road roar.
• We’re using an ipod as the source, not a vinyl record deck with plutonium wiring and a 50’s tube preamp bought from a bearded gentleman at the swap meet.

Nevertheless, I did have some doubts about possible quality loss, so I plugged the transformer into just one channel and left the other. I played a load of different music (Smashing Pumpkins, Mozart Piano Sonatas, Natalie Cole, Art Pepper jazz) and could not detect any loss in quality from one channel vs the other.

Finishing up

The wiring takes a bit of effort to stuff into the crevices of the dash and clear the area directly behind the head unit, so it locates into the mounting frame correctly. There’s a surprising amount of room either side of the ash tray, effectively in the footwell.