I don`t know about a Focus but on some modern motors entertainment systems are controlled by ECU`s and are often paired with dashes as a unit, some are linked to your ABS module to automatically increase and decrease volume as you increase and decrease speed and in my opinion you tamper with them at your peril if you don`t have the correct computer to sort out issues like yours. My advice is to get rid of the stuff fitted and reinstall the correct system for your motor.
cdc
September 2016