sam on my system
i run two head units
12+,grnd,aerial are spliced
but
the second head unit uses the first as the master for the speakers
so speaker outputs on the second head run into a Line Output Connector (Halfords Autoleads PC1-601 Line Output Connector £7.99) this drops the signals down so i can use the line in on the 1st head unit, which then uses the existing speaker system
i run two head units
12+,grnd,aerial are spliced
but
the second head unit uses the first as the master for the speakers
so speaker outputs on the second head run into a Line Output Connector (Halfords Autoleads PC1-601 Line Output Connector £7.99) this drops the signals down so i can use the line in on the 1st head unit, which then uses the existing speaker system