It only takes 2 screws to remove the bottom panel of a CM5905 or CM5907 Radio. There you will find the code jumpers; these jumpers, based on how they are soldered determine the radio code. Note where the jumpers are numbers 1-6 and 1-8 for each model of radio.
Solder the CM5905 jumpers like this to set code 15432:
Solder the CM5907 jumpers like this to set code 12422:
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Thank you for this post, as it has allowed me to revive two radios.
For those looking, the CM5905 instruction works on the CM2190 found in the Mercedes of the same vintage.