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Assistance with COMAND 2.5 Wiring for Aftermarket Stereo
I've purchased an aftermarket stereo to replace my malfunctioning COMAND 2.5 unit, and am having a couple of problems with finalizing the installation.
My aftermarket unit is a Seicane unit, and I have it powered, MOST box properly set up (for audio), rear view camera, navigation seemingly all functional.
I'll deep dive into each one, but overall, the remaining problems are:
Inability to tune FM stations (I hope to use the existing FM antenna)
Apparently draining the battery overnight.
Attempting to use existing stock bluetooth mic (so I don't have to run my own wire)
For context, I'm referring to the following wiring diagram which I think I found from this forum:
PROBLEM 1: Weak FM radio signal.
The reason is that I do not have an FM antenna connected to the stereo. Why? Because I hoped to use the existing FM antenna wired to the car; from the above diagram, I was hoping to find a double-white Fakra cable in my R-class. The picture I took when I removed the COMAND did not indicate that this cable was even connected? Unless it somehow got unplugged while removing the stereo and is somehow dangling down inside?
My thoughts for remedying this are a) figure out where the heck the double Fakra is inside my R-Class and connect it to the stereo OR b) buy an aftermarket passive FM antenna and plug it into the stereo (and bypass the car's built-in wiring). Option C might be to try and use the GPS (Blue) or Bluetooth (Yellow) Fakra connectors to serve as the FM antenna, but I'm dubious this would work as my trials have been unsuccessful.
Any other options?
PROBLEM 2: Battery drain overnight.
According to the manufacturer, the MOST box (to continue using the factory amp and HK optical audio) needs to be wired as such, and to which I wired the MOST leads to block A pins 12, 15, and 16, respectively (or more accurately, to the wires on the block A harness via vampire clips).
Unless it is a strange coincidence that my battery went dead overnight, it appears something is awry in this approach?
For the third problem, the stereo has a built-in 3.5mm mini-stereo jack, and they provided a mic I could wire myself into the vehicle, but I'd rather just use the existing bluetooth mic that I presume is already wired in the car. Now, the original stereo had Blue, Green, and Yellow connectors. Green is what is making the reverse camera work. The Bluetooth Fakra connector (Yellow) is a Bluetooth antenna, correct? Not a bluetooth audio Mic... Which means in order to use any existing mic, I'm probably looking at making my own harness for the COMAND block B wires, correct? If I solder leads from the block B harness to a 3.5mm mini stereo jack, which block b pins go to (presumably mono) 3.5mm pinouts?
Suggestions and tips most appreciated!
P.S. First time post to MBWorld, hope I did my homework
Last edited by khanklatt; 05-27-2018 at 01:29 AM.
Reason: Typo corrections
To problem #1, from looking at other threads, it would seem that the car antenna needs to be powered, and that the motorola-fakra cable they sent me doesn't provide power.
Now, this is the wrong headunit, but it does show (cable marked 30) a Fakra with a green power lead.
On this diagram, they show #7 being an ACC wire from the ISO port harness. Is it merely a matter of wiring 7 to 30's green lead and connecting the fakra to the factory fakra yellow or blue cables?
Option C will not work with any success, the band for FM 100mhz is extremely far off the wavelengths used for GPS and bluetooth which are in the gigahertz range and the antenna used for the bands must match physically to capture radio waves. Therefore you must locate the FM antenna connection that was originally used.
concerning your MOST box, connection to it from your new HU appears only to have left and right channels fed into it but HK is 8 channels so how will it be possible to recreate the sound of HK if 6 channels are missing?
i think you are going to have some dead speakers, and if not I suspect the sound will not be of the same spatial quality.
Are you going to have fader control as you had with your NTG2.5 HU? A center speaker driver?
The antenna power wire in the command is on block "B" Pin 7 . that needs to have +12v to power the antenna. Once the antenna is powered you should be able to connect the normal antenna fakra connector.
An aftermarket radio you will connect to the Amp control wire which when the radio is on should output +12v from it (see on the seicane diagram for Amp-Con wire #5 on the seicane diagram posted) . you can also just use a +12v ignition source but then the antenna will be powered even if the radio is off as long as the car is on.
For the Mic, you could tap into the factory mic from block B pins 1 or 2 and mic ground pin 9 the wires are there and that should work, but the mercedes has 2 mics, so you may want to tap both or just one of them.
Battery Drain overnight - possible coincidence. Just be sure the most adapter from Seicane is connected to ground, +12v constant battery and +12v ignition source (you may be able to use the Amp con wire on the seicane to power the most adapter for the acc connection)
The antenna power wire in the command is on block "B" Pin 7 . that needs to have +12v to power the antenna. Once the antenna is powered you should be able to connect the normal antenna fakra connector.
An aftermarket radio you will connect to the Amp control wire which when the radio is on should output +12v from it (see on the seicane diagram for Amp-Con wire #5 on the seicane diagram posted) . you can also just use a +12v ignition source but then the antenna will be powered even if the radio is off as long as the car is on.
For the Mic, you could tap into the factory mic from block B pins 1 or 2 and mic ground pin 9 the wires are there and that should work, but the mercedes has 2 mics, so you may want to tap both or just one of them.
Battery Drain overnight - possible coincidence. Just be sure the most adapter from Seicane is connected to ground, +12v constant battery and +12v ignition source (you may be able to use the Amp con wire on the seicane to power the most adapter for the acc connection)
There must be another wire used on the 2012 to power the antenna. "Block B" Pin 7 on mine doesn't even have a wire or pin there, only wires on 1-4 and 9-11 of that block. I wonder if anyone knows where that antenna amp is at so I can hard wire it.
There must be another wire used on the 2012 to power the antenna. "Block B" Pin 7 on mine doesn't even have a wire or pin there, only wires on 1-4 and 9-11 of that block. I wonder if anyone knows where that antenna amp is at so I can hard wire it.
Do you have HK?
from other posts Ihave read the audio gateway in the trunk has the tuners so thats were the antenna connection will be.
I know this is an old thread but with all the new head units coming up, it makes the change worth it. I’m running into the same problem, there is no double white fakra connector. There is a single but that’s for video in from the mmi in the glovebox. Not sure how the fm signal ever gets to the command. Wondering if anyone else has figured out this antenna issue. My next step will be to run a fakra cable and a +12 line from the tailgate to the new unit. Hate to tear apart the interior for a stupid cable that I’m sure is there somewhere.
I know this is an old thread but with all the new head units coming up, it makes the change worth it. I’m running into the same problem, there is no double white fakra connector. There is a single but that’s for video in from the mmi in the glovebox. Not sure how the fm signal ever gets to the command. Wondering if anyone else has figured out this antenna issue. My next step will be to run a fakra cable and a +12 line from the tailgate to the new unit. Hate to tear apart the interior for a stupid cable that I’m sure is there somewhere.
Check out this thread here for the fix which works well.
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Old 02-17-2019, 02:44 AM
#117 WaveyKat
I know this is an old thread but with all the new head units coming up, it makes the change worth it. I’m running into the same problem, there is no double white fakra connector. There is a single but that’s for video in from the mmi in the glovebox. Not sure how the fm signal ever gets to the command. Wondering if anyone else has figured out this antenna issue. My next step will be to run a fakra cable and a +12 line from the tailgate to the new unit. Hate to tear apart the interior for a stupid cable that I’m sure is there somewhere.
What car, and is it HK? My W211 had HK and the fakra connection is at the audio gateway in the trunk area. Had to run a cable back there to get FM reception.
What car, and is it HK? My W211 had HK and the fakra connection is at the audio gateway in the trunk area. Had to run a cable back there to get FM reception.
Hi there, I am running into the same issue with 2009 W211 with HK/Navi/Satellite radio. On my original NTG2.5, I only had 2 Fakra antenna connections a blue and a mustard. Blue i believe was radio/satellite/GPS and mustard was the bluetooth. I connected the new HU Fakra to the OEM blue, but there was no radio. I found the audio gateway in the centre of trunk. Is this the blue connector in the pic attached? Everything else works on my new HU except for the radio.
I have run a Fakra connection but was not able to open the black box to access this connector yet.
I am also trying to find out the wiring diag for block B. There are 2 sets of bundle wires.
One for the factory Mic and the other is just 2 wire bundle which i have no clue. Do you know?
Thanks in advance.
I wonder what is the best way to tie two mics into one input. Use a TS (mono) 3.5mm and wire both pins 1 and 2 to the tip and the shielding to ground pin 9. Or, use a TRS (stereo) and wire one signal (the tip) to pin 1 and pin 2 to ring 1 and then the third ground to pin 9. I am guessing the first setup as I know the mic that came with my stereo is a TS. Not sure how that would work out.
I wonder what is the best way to tie two mics into one input. Use a TS (mono) 3.5mm and wire both pins 1 and 2 to the tip and the shielding to ground pin 9. Or, use a TRS (stereo) and wire one signal (the tip) to pin 1 and pin 2 to ring 1 and then the third ground to pin 9. I am guessing the first setup as I know the mic that came with my stereo is a TS. Not sure how that would work out.
Did you work it out? I have the same question would like to use OE mics
05-27-2018, 12:09 AM
