Metra 70-1786 Radio Wiring Harness Compatible with Mercedes 1994-2004 & Land Rover 1999-2004 - Easy Car Stereo Installation for Seamless Audio Upgrade

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!