Does your base system include amplifier/tweeters or not?
There seems to be some mixups from time to time because in some countries the "base" stereo is 676 hifi, when the real base setup is the business audio without amplifier and no tweeters. If you do have the base system without tweeters and amp, you must run new wiring for underseat woofers so the mid speakers and woofers are not connected together anymore.
I used these plugs when replacing my base system with Match UP 7BMW and Audison speakers:
The ones with looped wiring keeps the connection intact to door speakers and the other ones are plugged to subwoofers and you can run the new wiring from these to the new amplifier.
Base system does have some equalizations done to compensate the missing tweeters, so if you install tweeters & amp you must code headunit to hifi, either by adding 676 to VO or manually changing these lines via FDL coding:
Code:
AMPLIFIER_VARIANT external
AUDIO_SYSTEM hifi