I work as a hardware/software engineer. So I could use the infrastructure from the company.
With this possibilities was it easily to make the small pcb for the display-unit extension or
to find the sources for the electrical equipment.


If this is the case then you really should consider making this available as a kit. I bet you would sell more than you think.
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'a stock car stereo is a beautiful thing to waste' MKIIa 60gb MKIIa 20gb