Audio Systems: After Market car stereo in VW, car audio manufacturers, vw jetta

Question
It is a 2000 VW Jetta 1.8T
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Followup To

Question -
Auto technician told me today that after market car stereos in volkswagens cause electrical problems.  If any diagnositcs are to be done the stereo must be removed.  Also stated that any auto electrical shop or dealer would make you remove the car stereo before running diagnostics.  He stated this is common with VW and Audi.  Why do car audio manufacturers make wiring harnesses for after market install?  Is what he is saying true?

Answer -
what car is this ?

Answer
no it is not true , you can do anythin on that car the radio have nothing to do  with the rest of the system   
you are going to need stering whell adaptors to keep that working but besides that everything will work just fine next time someone tells you something like that tell them to put it in writing