Mercedes radio gone to safe mode

[c250 turbo diesel]

Hi all, I have just taken a Mercedes radio cassette model sound 4000 out of a 310 sprinter, and put in a 316 sprinter, It fitted straight in, and I entered the code, all worked ok, but on switching off the ignition, and then back on, the radio has gone to safe mode, (Just says SAFE on the display,
As I have no instructions, does anyone know how I get out of this, any amount of button pushing will not change anything ! Thank's Roy

 

[190]

Don?t know about the Mercedes radio but the Rover radios you have to leave the ignition on pos 1 with the radio on for 15 mins and then renter the code. Sounds as if you don?t have the memory wire connected (permanent live feed)