The Becker radio on your car has only 2 outputs because they have to feed through the thumbwheel fader control for 4 speaker operation. To bypass this fader, remove the wooden trim panel, locate the rear speaker wires and extend them to the radio area. The front speaker wires can usually be found behind the radio via two DIN receptacles, round shape w/ 2 conductors, polarities are marked right next to the pins. The power antenna wire is usually blue w/ female tab connector, ground is brown wire and etc.