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I just installed a new cheap radio in my Mercedes since it was lacking one completely when I purchased it. It has ISO plugs, and the headunit I purchased was also ISO, so I figured it would be plug and play, even if I might lose steering wheel controls. However, the radio only works when the power is off. If I start the car, the radio is dead (no clock), I power off the car, dead, the lights go out... and 5 seconds later the radio power up and plays. It is mind-boggling. I tried it a couple times and it did it every time. The wiring looks correct, so it really is puzzling. Any help would be appreciated, thanks.
 

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I just installed a new cheap radio in my Mercedes since it was lacking one completely when I purchased it. It has ISO plugs, and the headunit I purchased was also ISO, so I figured it would be plug and play, even if I might lose steering wheel controls. However, the radio only works when the power is off. If I start the car, the radio is dead (no clock), I power off the car, dead, the lights go out... and 5 seconds later the radio power up and plays. It is mind-boggling. I tried it a couple times and it did it every time. The wiring looks correct, so it really is puzzling. Any help would be appreciated, thanks.
For your A-class? You need to provide a lot more information.

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The existing connector is not ISO - it's a Quad-Lock.

As I mentioned before on a different subforum, you're much better off getting a model-specific head unit, i.e. one designed for W169 / W245 / Sprint, et al - perfect fit, full connectivity and looks great - otherwise the cheap kit of a standard Double-DIN unit will require connectors, adaptors and frames, which in the end will cost more, than a model-specific unit.

At the very least you now need a converter: ISO to Quad-Lock ... could be up £60.

A perfectly specced modern android HU, with all the functions (including full steering wheel controls) is about £250, if that ...

There are two wires, that supply power to a head unit in Mercedes car (most of, anyway) - that's why it works when the ignition is off, but the key is still inserted.
Your ISO plug is obviously wired differently. Do you have a CANbus decoder box in the kit? If not, that's another rather expensive addition, if bought on its own.
 

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For your A-class? You need to provide a lot more information.
Yes, my 2005 A180. The VIN decoder indicates it has an Audio 20, but I thinks it's an Audio 5 from my research. And the power issues is likely a can bus deciding error. It has an ISO plug stock, not quad-lock, and it's only a single DIN, which goes against virtually all the other examples out there.
 

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Discussion Starter #5
MB•David;17844202 said:
The existing connector is not ISO - it's a Quad-Lock.

There are two wires, that supply power to a head unit in Mercedes car (most of, anyway) - that's why it works when the ignition is off, but the key is still inserted.

Your ISO plug is obviously wired differently. Do you have a CANbus decoder box in the kit? If not, that's another rather expensive addition, if bought on its own.
It's definitely an ISO connector, it plugs right into the cheap head unit I bought as a bandaid. And the radio only works when the car is off AND the key is out. I only figured it out it was a functional HU because I heard it start playing static as I had locked the car and was walking away keys inhand. Crazy. It's gotta be a can bus deciding error for power supply since it has both a constant and ignition supply. Lots like a more expensive model with a built-in can bus converter or paying a pretty penny for the can bus integrated wiring harness.
 

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The factory fitted connector is Quad-Lock.
If you have anything different, then someone had messed with it before, I'm afraid.

Without knowing what has been done exactly - was the original harness plugged into something else, or cut off entirely, any wires or pins re-purposed, etc? - it would be nigh on impossible to suggest anything meaningful, other that testing every pin to see if it matches the new head unit pinout.
 

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Discussion Starter #7
MB•David;17845180 said:
The factory fitted connector is Quad-Lock.
If you have anything different, then someone had messed with it before, I'm afraid.

Without knowing what has been done exactly - was the original harness plugged into something else, or cut off entirely, any wires or pins re-purposed, etc? - it would be nigh on impossible to suggest anything meaningful, other that testing every pin to see if it matches the new head unit pinout.
I understand, but the wiring looks factory, no cuts, still fabric wrapped, everything. I figure, since my car was an early production 05, maybe they used the ISO harness with the single DIN audio5 radio. My little mystery.
 

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Ah! - Well, you may be right - I have never seen Audio 5 (and didn't realised your car originally had one) ...

Do you have a pinout for the new unit? Or, can you contact the supplier and ask which pins are power - there should be two and perhaps a trigger wire (I hope - it certainly the case for quad-lock).
 
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