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Registered 2007 SLK 350
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62 Posts
Discussion Starter #1
I'm installing a new head unit with DVD, and I need to connect into the parking brake indicator wire (apparently to lock myself out of watching The Simpsons on the interstate). I did a search on the whole site for "brake" and didn't find anything to do with this wire after going through 29 screens. Does anyone know where the best place to tap into this wire would be and what color it is?

I might as well also ask where a good spot to tap into a 12v ACC wire would be, since that's my next search, although I would think the existing harness would have that connection...

Thanks in advance!
 

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Registered 2005 SLK350
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2,204 Posts
I agree with @efair as I have seen from two different manufacturers that required the parking brake connection. In one case, all that was necessary was tapping it to ground and the system always worked while the other system did require actual connection to the parking brake circuit. So, try it to any known good ground and see if it works. If not, keep looking for the needed wire.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,606 Posts
The last stereo I installed (Pioneer NEX) had a setting to control what to expect - ground or battery - on this wire.
 

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Registered 2007 SLK350
Joined
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525 Posts
I'm installing a new head unit with DVD, and I need to connect into the parking brake indicator wire (apparently to lock myself out of watching The Simpsons on the interstate). I did a search on the whole site for "brake" and didn't find anything to do with this wire after going through 29 screens. Does anyone know where the best place to tap into this wire would be and what color it is?

I might as well also ask where a good spot to tap into a 12v ACC wire would be, since that's my next search, although I would think the existing harness would have that connection...

Thanks in advance!
What head unit are you replacing?

Available wires in the harness will depend on that.

All signals are available on the CAN BUS (hand brake, ACC, Speed Pulse, lighting) but you will need a decoder to access them.
 

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Registered 2007 SLK 350
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62 Posts
Discussion Starter #7
It's just the R171 base model head unit (not sure of the model number). Not the HK. I took out the ashtray in favor of the other tray, so I think I can grab the old line from the lighter for my ACC - I don't think it is live all the time. Crutchfield says I can grab the parking blue/white brake wire at the base of the brake handle, but they believe the reverse wire has to go back to the trunk/boot because I need to grab the gray/yellow wire on pin #8 of the 14 pin plug at the trunk fusebox. I can grab that easily enough once I get into the trunk, but I still haven't found an accessible route. I've seen three alternative routes; the one that goes through the hinge area scares the bejeezus out of me because I don't want to chew up my wires. The other two methods seem to leave out critical steps that leave them unworkable (at least for me). Thanks for weighing in!
 

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Registered 2007 SLK 350
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62 Posts
Discussion Starter #8
What head unit are you replacing?

Available wires in the harness will depend on that.

All signals are available on the CAN BUS (hand brake, ACC, Speed Pulse, lighting) but you will need a decoder to access them.
forgot to tag you on my reply above.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,606 Posts
I've not replaced the head unit on an R171, so I'm no expert, but have you checked for an adapter to convert all these signals?
 

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Registered 2007 SLK 350
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62 Posts
Discussion Starter #10
I have an adapter for most everything else. All plug and play from Crutchfield. Since the old head unit had no reverse camera or DVD, MB didn't provide any connection for those in the original harness so I have to track them down separately. The power seems like it should have been fairly easy, but for whatever reason Crutchfield wants me to grab it from somewhere else. No big deal.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,606 Posts
That is truly odd that you can't find the correct power in the factory harness. By "adapter" I don't mean a "wire adapter" but a little black box that requires power and that connects where the old A20 radio CAN connected (connector 2 pins 9 and 11) and that translates the reverse and parking CAN signals into wires you can attach to your radio. They usually cost 50-100 USD, but they save you the agony of routing wires through the car for these signals.

BTW, the only access hole that I know of between the passenger cabin and the boot is near at top of the B-pillars. My preference would be the side opposite the fuel filler.
 

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Registered 2007 SLK 350
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62 Posts
Discussion Starter #13
@Oregon Bob - Not sure if you still need it, but here is a picture of the parking brake light switch. See attached: R171 Picutre Parking Brake Switch S12.pdf
Thanks! I'm still trying to get the stupid tunnel cover off. Got the forward two screws out. Got the vertical compartment off. Got the nut off the bolt in the horizontal compartment. Just can't figure out how to get that stupid lid hinge out of the way! Once I get the tunnel cover out, your picture will be very handy. Thanks!
 

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Registered 2007 SLK350
Joined
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525 Posts
That is truly odd that you can't find the correct power in the factory harness. By "adapter" I don't mean a "wire adapter" but a little black box that requires power and that connects where the old A20 radio CAN connected (connector 2 pins 9 and 11) and that translates the reverse and parking CAN signals into wires you can attach to your radio. They usually cost 50-100 USD, but they save you the agony of routing wires through the car for these signals.
This was what I suggested earlier :whistle:

This will save you all the trouble of finding feeds splicing in wires and routing cables.

Also will convert MB connector to ISO for speaker connections

CANBUS

and this one also interfaces with steering wheel controls if your head unit supports it.

CANBUS and steeringwheel controls

If you have COMAND with fibre optics then there are other interfaces.

Totally plug and play, all wiring behind the head unit :)

Other similar products available, but I have used products from this company and no hesitation to recomend.
 

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Registered 2008 SLK350
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2,243 Posts
Thanks! I'm still trying to get the stupid tunnel cover off. Got the forward two screws out. Got the vertical compartment off. Got the nut off the bolt in the horizontal compartment. Just can't figure out how to get that stupid lid hinge out of the way! Once I get the tunnel cover out, your picture will be very handy. Thanks!
See vid.From 4:05 onward.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,606 Posts
Did you get the two nuts at the top? Hint- use a magnet to avoid dropping these!
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,606 Posts
That video is missing some information, at the very end it shows a steel bracket, this bracket must be unbolted from the firewall before you can remove the console.
 

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Registered 2007 SLK 350
Joined
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62 Posts
Discussion Starter #19
Did you get the two nuts at the top? Hint- use a magnet to avoid dropping these!
Yes, I did get them, but I didn't drop either nut down there. I did drop one of the screws from the top of the unit however! Hopefully I can find it when I pull the whole unit! Good tip though!
 

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Registered 2007 SLK 350
Joined
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62 Posts
Discussion Starter #20
That video is missing some information, at the very end it shows a steel bracket, this bracket must be unbolted from the firewall before you can remove the console.
I saw that, That's what confused me. I got it unbolted, but it's unclear if I need to totally pull it out before I can pull the tunnel. I'll get out there in a bit and wrestle with it. Thanks!
 
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