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Discussion Starter #1
I posted this info on another site about a week ago, but since I've also used this site for information, I thought I'd share my findings here too. I may have scared people off on the other site because my post was too "wordy" but oh well. I did my part to share info at least. I'll keep it short here though.

I originally wanted to make a pcb version of a roof controller, but it was too expensive to print a one-off board. So once I understood what I needed to do, I decided to use some common auto relays. This makes it much simpler for guys who are not too tech savvy to put together a pcb, but can at least tie some wires together. And I only cared about two things anyway: The one touch function and opening/closing the top at speed. This allows that.
For the one touch you will need…

2. SPDT 12V Relays (The ones with 5 blades instead of 4) Make sure they have 87 & 87a. RL45’s at Auto Zone (The blazer brand ones at autozone have two 87 ports and are useless)
1. Pack of wire splices (The blue ones that let you connect a wire into another without cutting it). Get the smallest gauge pack you can find. The 16-18 or something like that.
1. Pack of female .250” blade terminals. Again, find the smallest gauge pack.
1. Roll of 14g or even 16 gauge wire. I used 12g for mine which proved useless and took up more space. The original wires are so thin anyway. And only supply a signal, not the actual power for the top.
Then supplies…electrical tape, pliers to crimp the terminals and splices, and if you wanna get fancy, heat shrink tubing, soldering iron, an inline fuse, and some patience.
All in all, the bare minimal should cost you around $30 (depending on your area and extra stuff if you hoard stuff like me).

How it works… NOTE: THE WIRE COLORS ARE FOR ILLUSTRATIVE PURPOSES ONLY. YOU CAN MAKE THEM ALL BLACK IF YOU PLEASE. Looking at the diagram, you see that flipping the switch in either direction will provide ground to either the blue or green circuits, so only one relay will be activated at one time. This triggers the relay to allow power to flow from 30 to 87 on the active relay. The bridge from 87 to 85 allows the relay to remain powered even after you release the switch because the green/red wire that is associated with the switch lamp provides ground until the light goes out. However, this relies on the fact that this ground signal will always require the opposite relay to be inactive thus allowing a flow from 30 to 87a. When you flip the switch in the opposite direction during operation, both relays are active, thus removing the 30 to 87a flow needed to power either relay. This allows you to flick the switch to stop the top and even close it if you change your mind. Nifty. One thing to note…because the original harness is so thin, the wire splices just pinch the wire and don’t always make a strong connection. I had to manually open each one and pull the wire sheathing apart to expose a bit of wire so the teeth of the splicer can make good contact. I hope that made sense. Just use a multimeter if you’ve got one to make sure the connection is established correctly. Leave some long leads coming off of the relays so that you can make the connections on the right side (this is all done under the gear selector trim that holds the window switches) but run the wires behind the shifter and into the left side where you can tuck in the relays out of the way. I hope that made sense.

ON TO THE SPEED LIMITER!
I knew that 74 and 56 supplied speed information to the module. I just didn’t know how. I took a leap of faith knowing cutting both wires. I tried connecting them directly to ground. Nothing. Directly to power. Nothing. Then with my multimeter on “beep mode” lol… I realized that the 56 coming from the car harness was “pulsing” with the car parked. Wire 74 was not. Just solid ground. SO…… I knew a resister would change the voltage and I didn’t want to wait for one from ebay, so I took apart an old radio and cut one out. I found was one that measured 620. I then left the 74 lead unconnected to anything and put the resister inline from incoming 56 to the 56&74 that go to the control unit. Took it out for a drive and damn-it, it worked! It works up to about 45mph. Any more and the switch won't activate the top. So yeah, the 74 should be the 5th wire from the right at the back passenger side corner. It’s Green/White. 56 is on the next row over and two pins forward. Blue/Green. Be careful, there is an identical wire further ahead at another pin so follow the correct wire on the loom carefully. But these are the same two wires you’d end up cutting for a module anyway.
 

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Discussion Starter #2 (Edited)
Diagram

Here is a very crude drawing of what I meant about the relay locations. I hope pelican parts doesn't mind me borrowing their image. No, it's not to scale, and doesn't show all the wires. It just shows where everything goes so that it will fit.

EDIT: I am attaching an old photo of how I tied together the wires to bypass the speed limiter. The resistor is in the heat-shrink wrapped wire in between. No, I did not leave it in there like that, that's just a photo of when I was "testing". You can see how the green wire (74) is left unconnected.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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Can you give the details on where the red, green, brown, and blue are connected?
 

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Discussion Starter #4
Can you give the details on where the red, green, brown, and blue are connected?
Sure. As mentioned, I just made them those colors for visual purposes. You can use any color you want. And I wrote the colors of the wires they connect to in the image. But in case it's blurry...

Red - Red/Pink/Black Band
Green - White/Purple
Brown - Green/Red
Blue - Green/Purple

The first color is the main wire color and the second is the stripe color.
 

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Discussion Starter #5
Can you give the details on where the red, green, brown, and blue are connected?
And in case I misunderstood, you may be asking about the black hashes. Those are the relay poles they connect to. They have numbers on them. Here is an example...
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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I mean, how do you connect to the car? It's got to attach to the roof switch somehow (or am I missing something?)
 

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Discussion Starter #7
I mean, how do you connect to the car? It's got to attach to the roof switch somehow (or am I missing something?)
It is simply piggy-backing into the existing wires. You just splice them into the lines and the relays will take care of the rest. Those wires... the red/pink, white/purple, green/purple, green/red are the wires coming from the switch and feeding into the roof control module. The red/pink gives 12v to the switch light and if all criteria is met (truck roller blind and etc), then the module allows Ground current to flow from the green/red(Ground) into either the white/purple(Up) or green/purple(down) to operate the roof. When the ground current is flowing through the switch, it also lights up because it already has a 12v signal (red/pink). We are taking advantage of the fact that the light remains on the entire operation of the roof. So this maintains power to the appropriate relay in order to do it all with one press instead of holding the switch. The double click for windows function still works, you can stop mid operation and close instead, and you don't cut any wires. You just splice into them. Hope that helps.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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I see, thanks. This is most impressive, and I will try it on my next project R170. Probably later this year.

Running just one wire from the fuse box run to the apparatus box would allow this mod to be done entirely in the apparatus box and without disassembling the console, right? That seems like less work than disassembling the console.
 

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Discussion Starter #10
You will need to connect all four wires, and yes, this could work connected in the Ecu box instead, but I don't know if there's enough room in there for the relays. Maybe. I haven't checked but didn't want to add more wires/heat/mess to that crowded place. And taking the console plate off is not difficult at all. Pelican parts has a write up on how to do it. And yes, it holds the circuit open. Make sure to add the resistor in the ecu box too. It's really worth the effort to be able to power the top on the go.
 

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Registered 2005 SLK350-sold
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You will need to connect all four wires, and yes, this could work connected in the Ecu box instead, but I don't know if there's enough room in there for the relays. Maybe. I haven't checked but didn't want to add more wires/heat/mess to that crowded place. And taking the console plate off is not difficult at all. Pelican parts has a write up on how to do it. And yes, it holds the circuit open. Make sure to add the resistor in the ecu box too. It's really worth the effort to be able to power the top on the go.
Again, excellent idea, perhaps a solid state relay would be better/smaller. I would guess that current is minimal, I wouldn't think the actual power for the top pumps go through the switch, only the signal to the car's computers.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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1978L82

please post a quick introduction to our members (see my message) :D

Join the gang! Your 1st thread should be your introduction so we can welcome you properly so post an introduction in the ‘New members introduce yourself here’ section, if you haven’t already. New Members Introduce Yourself Here - Mercedes Benz SLK Forum
 

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Discussion Starter #16
Yes, I've thought of this myself. Until I find a way to do it with the original fob though, the next best thing may be a $30 remote start kit from Walmart. It'll be on a seperate fob, but it should work.
 

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Premium Member 2001 SLK320
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Disable switch?
And to disable this one touch function, just like the 'modules' do, one just splices a switch in line on the red wire near the fuse and mounts the switch somewhere out of the way ? Am I correct?
Then someone unaware of the one touch feature can't accidently activate it.
Of course this might add another $5 investment.

Change speed limit
Is there a simple way to set a lower speed limit? 45mph sounds quite high. Would significantly changing the resistor do it?

Windows, clarification please
Also, You say "The double click for windows function still works", what exactly does this mean?
- that holding the window switch down to the second stage, click, it drops all the way hands free, or
- double click the roof switch and both windows drop, or raise

1978L82 your solution is just so elegant in its simplicity, low cost and easy installation.
 

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...red/pink gives 12v to the switch ...
...We are taking advantage of the fact that the light remains on the entire operation of the roof...
I never noticed a light at all, I guess my hands cover it when using it. I will check that out, off to the manual!
And assuming that light is on while the top is moving and turns off automatically when at either end, even when you have the switch manually pressed, using that to hold the relay is genius (well, not GENIUS, but a REALLY great idea)

Edit: Maybe the R170 is different, need to look some more. I don't see any reference to a light on my R171
 
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