[particlewave]

Originally Posted by Paul

The radio security wire should not be grounded.

Always test for current with a test light, a voltmeter is useless. Connect the light to your power and ground sources.

Yes, the brown/blue wire needs to be grounded or the alarm will sound.
Pelican Technical Article: Changing Your Boxster Stereo Head Unit / Installing Boxster Ipod Integration - 986 / 987

Take it from an engineer; a "test light" is antiquated and doesn't tell you anything about power (actual current and voltage), only that you are completing a circuit. A multi meter is much more useful.