I bought this wiring harness to install a new radio in my Mercedes 2003 SLK 230. It's the right piece!I don't know about other Mercedes' by my SLK 230 required switching of Yellow and Red wires (it might be for others too). It's a battery constant and ignition. Also, I installed SONY stereo. Now the thing here is that it will depend on stereo whether it will turn on or not without ignition. The way these new stereos are designed is that they won't turn on if you don't turn you ignition on, so you don't forget to switch your radio off and save your car battery =) I was really confused about that. Of course, you can connect without the ignition wire, so it's always stays on, but I don't mind keeping my key in position 1 when listening to radio. This way I know that I won't forget to turn my radio off. The ignition function is a memory for new radios, so it saves your presets and settings.In addition, on SLK 230 there are only two front speakers! (Rear ones are low-frequency, aka subs) They way Mercedes designed(I don't know why) their amplifier is that front and rear speakers are connected parallel and the amplifier does all the job - automatically allocating low and high frequencies to back and front speakers. Stupid, right?! It took me a lot of reading to understand.So, if you take the bottom pinout, all you need is 2 pair of wires in the middle (left and right speaker) and you don't need left and right. Blacks are negative and color-coded are positive. (This is for SLK only. My friend had a 4-door sedan and he needed all of them!). After installation just go to settings and set everything to FRONT or ALL but not the back. (you will hear nothing ig you set it to back =) )One more thing, when you connect via RCA plugs you may hear an annoying popping sound every time you play with the menu or switch it on or ofF. Don't get scared! I simply cut off the RCA plugs and soldered it to my new radio harness speaker wires. (Hint: cut off pins from RCA plugs so you can solder them on to your new radio harness and put them back in place into plastic harness assembly so it looks neat) You Don't need to cut any of your stock harness!Biggest pro of this product is the fact that I did not have to cut into any of the OM wiringCon was definitely the fact that I had to remove the RCA cables and wire speakers directly into the aftermarket stereo harness (it's really not that big of a deal the bottom of the RCA cables are color coded wires for example green/black, white/black, purple/black so solid color is positive and black wires are negitive)*PS those folks who have the 3 plug audio system in w124s THE TOP PLUG IS LEFT ALONE... It gets tucked away. Only plug you have to worry about is the double plug*I'm very happy with this product. Gone are the days of hacking up the stock wiring harness as I'm sure we all have had fun with over the years. I changed from the stock stereo (Benz tape deck) to a JVC unit with Bluetooth. I looked at the harness and checked it to the stock harness to make sure power and ground all lined up, and they did. I tested with a test light stock power and constant power and they matched up perfect to this harness layout. Wired the new stereo harness on my kitchen table with my son and walk to the car, plugged it in and started the car. Power and sound all perfect! (Notes-- the speaker out on this harness has RCA adapters and the new stereo harness did not. So to avoid hacking this new conversion harness I used 2 of these, ((((2 of Rockford Fosgate RFIF2SW Speaker Line to Female RCA Adapter))), to wire clean and correct. Plugged right in color to color and fade and balance all work perfect!I ordered this for a 1998 Mercedes C230, so the plug from my original car radio fit and plugged into this unit I connected all the power wires to my aftermarket radio turned on so that was working fine now the RCA plugs are a problem, when i plugged them in my after market radio the sound did not work tried plugin them in a different order still nothing. So I had to cut the rca's off split the wires and connect them to my aftermarket radio which worked great after that i did have sound. So it might be better to order (Metra 70-1784 Radio Wiring Harness for Audi 88-99/Volkswagen 80-Up) which doesnt have the rca plugs it does say its for audi but the connections seem to be the same. But with this unit you might have to splice the rca plugs like I did which is not hard but you will have to find the negative and positive on these wires not hard either just play with it until u hear sound. The built quality of the unit is very goodIt works. I used it in my 97 mercedes e320. I had to cut off the rca cables so I could connect the speaker wires from the stereo individually. Everything works and sounds great. It would have been nice to have this same one without the rca cables, but I couldn't find one.Alright.....first things first. I used this on my Benz E 240 2002 and it wasn't an exact match. The car's +12 Memory and two more pins were not aligned with this harness slots. I had to pull out the Red wire (+12 Memory) and re-insert it to another slot to align it with the stock wires. To use my Sony CDX-GT500U, I didn't have to worry about the other mis-aligned pins. I joined the +12 Memory and +12 Switched together and then connected them to the +12 Memory of the stock wires. The Ground (Black) was aligned okay. I simply had to wire them together. Yes, the RCA sockets had to be cut off to make the speaker connections.It wasn't a tough job and I liked doing it. I cut off the RCA sockets and used crimp caps for wire connections and it made my work look very clean and professional. The wire color codes of this harness exactly matches the speaker locations on my car.Overall quality of this product is good. I'd recommend it.UselessWorked like a charm for my slk230 1998 MercedesShould have the antenna converter included. If you plan to use FM or Radio, you'll need the antenna adapter tooWell.... didn't work...had to wire it differntly...