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Discussion Starter #1 (Edited)
Though there is already an excellent post that covers much of this, there still seems to be some confusion about the stock bose audio system and how to install an aftermarket head unit. First, a few notes about the bose system and what to look for when buying an aftermarket hu (head unit).

The bose system is a bit wanky and there is only so much you can do with it. It is a power amp that drives all the speakers in your car. The input will only accept left and right signal feeds. This means you can't have front and rear fade controls. You're stuck with fairly anemic subs and an underpowered system in general. To substatially upgrade would mean removing speakers and the bose power system and starting from scratch.

This doesn't mean an new head unit wont improve the sound at all and adding bluetooth is certainly a feature most of us want. When shopping for a new HU, don't worry about buying a really powerful unit as you are only using the pre-amp to feed the hu. It is important that you buy one that puts out 4 volts (some are two) through the rca outputs as that's what you'll be using. Don't worry about 100 watts per channel as you wont be using any of that. Your just using the 4 volt outputs to drive the bose.

I used crutchfiled as they are price competitive and all the extra install gear needed was really inexpensive. I had some tehnical questions and they know their stuff. So when shopping, look for 4 volt output and the features you want (variable display color, bluetooth, usb charging etc). Now onto the install.

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Here is the install kit that came from crutchfield. The cool star thingies are to remove your factory HU.

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Here's where the star thinigies go. Typical benz. When the rest of the world uses side clips, Benz goes from the bottom. Anyway stick em in and it will release the hu and you pull it right out.

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You'll see all the various harnesses for telephone, cd changer etc. You'll only use the one pictured here and the antena lead.


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Now, let's go to the kitchen, heat up the soldering iron, open a beer (or thinking fluid as I call it) and get to work. The two rca plugs (white and grey) go into the jacks on the back. Make sure you plug them into the left and right jacks on your new hu and not the rears. You'll only attach five wires from the hu wiring harness to the adapter that crutchfield supplies. They power up the head unit and sends power to the bose power amp. All the signal to the bose is provided by the rca jacks. The are all color coded. I soldered mine and taped them to insulate them though if you're really groovy you can use heat shrink.

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This is the antena lead adapter which also came from crutchfield. You'll need this so you can use the antenna in the car. Once again, MB can't conform to most of the rest of the world but what the heck, it was about 20 cents.

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This is where the adapter goes on your hu.

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Now back to the car and lets test it out. The factory harness is plenty long enough that you don't have to install it to make sure it works. This is the point where you make sure it works. If you've done everything properly, a smile will show on your face and you may reward yourself with more thinking fluid as you're nearly done.

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Now, unplug the HU and lets install the din cage. It's the little metal bracket that will hold your new hu in place. Just push it into the opening and you'll here it click into place. Re attach the wiring harness, the rca leads and the antenna and push the hu into its new home until you hear it click into place.

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Voila. I hope this was helpful and you see how easy this is to do. The only tools you need are a wire stripper and a soldering iron. If you don't know how to solder, you can use those twisty things. Wire strippers are easy though practice on some throw away wire first until you get the hang of it. It took me 5 times as long to resize these pics and write this post as it did to install the new hu. Cheers and happy motoring.
 

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Premium Member 2001 SLK320/2000 SLK230
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Know this is oldish but a minor correction. While it is true the factory wiring accepts only front right and left channels, that is because of how it is wired at the AMP.

The amp itself has front and rear, they are just bridged in the harness. So you can get front/rear fading but need to rewire the HU-amp harness.
 

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Discussion Starter #4
Know this is oldish but a minor correction. While it is true the factory wiring accepts only front right and left channels, that is because of how it is wired at the AMP.

The amp itself has front and rear, they are just bridged in the harness. So you can get front/rear fading but need to rewire the HU-amp harness.
I'm not brilliant at reading schematics, but it looks like there are only two paths going to the power amp. How exactly would you re-wire the harness?
 

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Discussion Starter #5
Know this is oldish but a minor correction. While it is true the factory wiring accepts only front right and left channels, that is because of how it is wired at the AMP.

The amp itself has front and rear, they are just bridged in the harness. So you can get front/rear fading but need to rewire the HU-amp harness.
Still curious how to do this.
 

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Premium Member 2001 SLK320/2000 SLK230
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Simple: wire the eight connections on the amp to the eight (F-R, L-R & grounds) on the new head unit instead of only the four fronts. This will require a new eight wire HU to Amp harness for the speakers.

Exactly what wires go where depends on the selected head unit.

Here is the Amplifier connections (numbers refer to diagram I posted: (sub ~ rear)
AMP pin 10 - Right Sub input (+)
AMP pin 9 - Right Sub input (-)

AMP pin 1 - Left Door input (+)
AMP pin 2 - Left Door input (-)

AMP pin 7 - Right Door input (+)
AMP pin 6 - Right Door input (-)

AMP pin 8 - Left Sub input (+)
AMP pin 3 - Left Sub input (-)
 

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Looks like I can tackle this. I really don't care that much about front to rear capability, so it'll be a standard install, as long as I get the correct HU. I didn't see you mention anywhere about disconnecting the battery before beginning. Not necessary in this case?
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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If it was not mentioned, make sure you have the radio code/if oem radio before disconnecting the battery
 

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Looks like I can tackle this. I really don't care that much about front to rear capability, so it'll be a standard install, as long as I get the correct HU. I didn't see you mention anywhere about disconnecting the battery before beginning. Not necessary in this case?
Though there is already an excellent post that covers much of this, there still seems to be some confusion about the stock bose audio system and how to install an aftermarket head unit..
Know this is oldish but a minor correction. While it is true the factory wiring accepts only front right and left channels, that is because of how it is wired at the AMP.
Multi quote for the benefit of @tsberkey

I presume his question is for one of you guys.
 

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If it was not mentioned, make sure you have the radio code/if oem radio before disconnecting the battery
I was reading the manual (GASP!) and I saw that about the radio code. I took a picture of the code card so even if I lose it, it's in my Google Photos! Thanks for the heads up, Jeff!
 

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OK, important point. As stated I made a jumper cable to go from the factory harness to the radio. No cutting of factory harness needed. When time to install it was just unplug one connector and plug the other in so battery disconnect was not needed.

OTOH if you are of the cut-n-splice school, disconnection would be a very good idea since the keep-alive is always hot.
 

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Discussion Starter #12
Looks like I can tackle this. I really don't care that much about front to rear capability, so it'll be a standard install, as long as I get the correct HU. I didn't see you mention anywhere about disconnecting the battery before beginning. Not necessary in this case?
No need to disconnect the battery.
 

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So, I ordered my HU from Crutchfield tonight. They are including this harness for free. Does this mean I won't have to do any of that splicing (or, less of that splicing)? A little confused by the four RCA jacks, but I'm sure it'll make more sense when I have it in my hands on Wednesday.

EDIT: I am assuming R and L, for both front AND rear, but the colors aren't what I was expecting to see.

EDIT 2: Never mind. They just emailed me the pdf for this connector. Now, it's clear!


 

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I don't understand the RCA plugs. Usually on a head unit the RCA plugs are for line output, not amplified but the Amp in a SLK is expecting the amplified output, regular speaker wires. Rest of the wires you splice to the Head Unit connector and this makes a jumper from the Merc harness to the Head Unit.

You may also need an antenna adapter

Hope it works.
 

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I don't understand the RCA plugs. Usually on a head unit the RCA plugs are for line output, not amplified but the Amp in a SLK is expecting the amplified output, regular speaker wires. Rest of the wires you splice to the Head Unit connector and this makes a jumper from the Merc harness to the Head Unit.

You may also need an antenna adapter

Hope it works.
Yeah, they're sending one of those, as well. Even if I have to splice five wires, it's not like I haven't done that a million times. Just never had to do it on a car stereo.

Thanks for the input. We'll know more on Wednesday.
 

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I see in an earlier post that they did use pre-amp inputs to the amp. That is not my understanding but never say never. I'd wire to the preamp outputs first and see what happens but both of mine reach levels sufficient for use with normal hearing at about 20-25% volume, 60 db down at 50%.
 

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Discussion Starter #17
I don't understand the RCA plugs. Usually on a head unit the RCA plugs are for line output, not amplified but the Amp in a SLK is expecting the amplified output, regular speaker wires. Rest of the wires you splice to the Head Unit connector and this makes a jumper from the Merc harness to the Head Unit.

You may also need an antenna adapter

Hope it works.
No, this is not correct. The bose needs the line output not the amplified output. Please read my install post as it's pretty clear. The main thing is to get a hu that puts out 4 volts. You'll use two of the RCA plugs into the L/R line outs of the head unit. The others wont be used.

You're not splicing into the factory wiring at all. You are splicing together the two harnesses you get with the kit. One is the universal one that comes out of the hu. You splice that into the harness that ultimately goes into the factory wiring harness.

You will need an ant adapter but as I recall, it came with the install kit.
 

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Discussion Starter #18
I was reading the manual (GASP!) and I saw that about the radio code. I took a picture of the code card so even if I lose it, it's in my Google Photos! Thanks for the heads up, Jeff!
I put it in my phone contacts under benz radio so I can find it fast.
 

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Discussion Starter #19
So, I ordered my HU from Crutchfield tonight. They are including this harness for free. Does this mean I won't have to do any of that splicing (or, less of that splicing)? A little confused by the four RCA jacks, but I'm sure it'll make more sense when I have it in my hands on Wednesday.

EDIT: I am assuming R and L, for both front AND rear, but the colors aren't what I was expecting to see.

EDIT 2: Never mind. They just emailed me the pdf for this connector. Now, it's clear!


You'll use the white and grey only. If you look at the 4th pic in the original post, I should be pretty clear. Sounds like you have soldering skills so this whole thing is a piece of cake. Don't overthink it.
 

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I really appreciate that and your writeup is great. One point you made has me wondering: "and an underpowered system in general".

Am hearing impaired, 60 db down and both of my R170s (real and clone) have amplifiers and 50% volume on both is enough for me to hear phone/GPS/music clearly unaided (with a passenger and hearing aids, 25% is "enough").

Know the clone is using the speaker outputs but real one had Bluetooth HU installed when I bought it however with a 2v preout doubt that it would be producing the volume it does if connected that way.

Finally, the stock radio that came with mine does not seem to have any line outputs, only speaker (C cavity on top is for the CD changer).

Be interesting to see what is found when you pull the factory HU

ps just got a note that the option code "810 - Sound System" for a R170 is for the Bose system.
 

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