Editing Z31/stereoinstall php (section)

==== *Common Ground ====

The GL models use a common ground system for the speakers. This means a common ground is shared between more than one speaker. The Z31 has this type of wiring from the factory—left side shares a ground and right side shares a ground. To wire your aftermarket head unit, you’ll need to split this out so each speaker has its own ground to the head unit.

An easy solution is to run new speaker wires to either the front or rear speakers and use the stock wiring for the other set. For example, you can keep the stock harness for the front speakers and run new wiring to the rear, which also keeps the Voice Warning System intact.