first the speakers are
NOT a common ground. Also, all aftermarket radios don't support common ground, please don't do it, you will blow up the amp inside whatever you put into it.
also, if they cut the harness after the aftermarket splicing, the wires will be the same color as the new harness, if not, try this:
http://www.installdr.com/Harnesses/VW-Wiring.pdf
Do
NOT connect all the wires to the aftermarket radio, you can cause a failure to the comfort control module or ecu.
ONLY connect the 8 speaker leads, 12v battery + unswitched, 12V ignition switched, ground, and dimmer (if the aftermarket radio has a dimmer lead).
I hope this helps!
