1998 Audi A4 Quattro rear speaker wiring

The brown wire from the downstream sensors is broken or otherwise not connected to the computer. Check for damage to the wire.

you must check wiring cable of left speaker-reconnect antenna cable and check if it is firmly connected and apply contact cleaner over faders.

Windstar Car Stereo Radio Wiring Diagram - All years
Car Radio Constant 12v+ Wire: Green/Violet Car Radio Switched 12v+ Wire: Yellow/Black Car Radio Ground Wire: Black/Light Green Car Radio Illumination Wire: Green
Left Front Speaker Positive Wire (+): Orange/Light Green Left Front Speaker Negative Wire (-): Light Blue/White Right Front Speaker Positive Wire (+): White/Light Green Right Front Speaker Negative Wire (-): Dark Green/Orange
Left Rear Speaker Positive Wire (+): Light Brown/White Left Rear Speaker Negative Wire (-): Light Brown/Yellow Right Rear Speaker Positive Wire (+): Light Brown/Green Right Rear Speaker Negative Wire (-): Brown/Pink

Speakers
1995-1998: 5" x 7" Front door and side panel 1999-2003: 6" x 8" Front and rear door

Have you removed the original connector from you original stereo? If you still have the original connector in place you can get a new connector from the Ford dealer that will plug into your existing wiring and into your new deck. Ford connections are unique to Ford and you need to adapt them for this application.

Take the car and deck to the dealer and tell them what you need. Everything just plugs in and your original amp and speakers in the car will work.

Having said that there was an adapter available at Wal Mart of all places that did work. You may want to check there.

If you have removed the original connector then you need a wiring diagram.

1992 Ford Probe Car Stereo Radio Wiring Diagram
Radio Constant 12V+ Wire: Blue/Red
Radio Switched 12V+ Wire: Blue/White
Radio Ground Wire: Chassis
Radio Illumination Wire: Light Green/Black
Radio Dimmer Wire: N/A
Radio Power Antenna Trigger Wire: White
Radio Amplifier Turn On Trigger Wire: N/A
Front Speakers Size: 6 1/2′
Front Speakers Location: Doors
Left Front Speaker Wire (+): Blue/Orange
Left Front Speaker Wire (-): Blue/Black
Right Front Speaker Wire (+): Blue
Right Front Speaker Wire (-): Blue/Green
Rear Speakers Size: 6 1/2′
Rear Speakers Location: Side Panels
Left Rear Speaker Wire (+): Green/Orange
Left Rear Speaker Wire (-): Green/Red
Right Rear Speaker Wire (+): Green/Blue
Right Rear Speaker Wire (-): Green

The amp is located under the rear passenger side window. You need to remove the plastic side wall to expose it if you need access there. You can trace the wiring if needed.

Under the front bottom edge of the rear seat are clips holding the seat in place. Open the clips and the seat lifts off. You can then get to the amp as needed.

look at crutchfield.com for free, they should be able to answer you're question...
Good Luck

1992 Saturn SL2 Car Stereo Radio Wiring Diagram
Car Radio Constant 12V+ Wire: Orange
Car Radio Ignition Switched 12V+ Wire: Yellow
Car Radio Ground Wire: Black
Car Stereo Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amplifier Trigger Wire: N/A
Front Speakers Size: 6 1/2′
Front Speakers Location: Doors
Left Front Speaker Wire (+): Tan
Left Front Speaker Wire (-): Gray
Right Front Speaker Wire (+): Light Green
Right Front Speaker Wire (-): Dark Green
Rear Speakers Size: 6 1/2′
Rear Speakers Location: Rear Deck
Left Rear Speaker Wire (+): Brown
Left Rear Speaker Wire (-): Yellow
Right Rear Speaker Wire (+): Dark Blue
Right Rear Speaker Wire (-): Light Blue

here is a diagram of the radsio connector wire colors in your car, just match them up to your Sony.
1998 Chevrolet Malibu Car Stereo Wiring Diagram
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Antenna Trigger Wire: Pink
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: 4′ x 6′
Car Audio Front Speakers Location: Doors
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: 6′ x 9′
Car Audio Rear Speakers Location: Rear Deck
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue
-->

If your factory wirig harness has been cut< take a 9 volt battery and touch diffrent wires, once you touch th negative and positive side of one speaker you will hear a small static sound out of that speaker. that may help you locate th speaker. and th brown will be your ground on each speaker

Radio Constant 12V+ Wire: White/Green
Radio Switched 12V+ Wire: White/Red
Radio Ground Wire: Black
Radio Illumination Wire: n/a
Radio Dimmer Wire: Red/Black
Radio Antenna Trigger Wire: n/a
Radio Antenna Location: Rear Glass
Front Speakers Size and Location: 6 1/2′ Doors
Left Front Speaker Wire (+): Blue/Green
Left Front Speaker Wire (-): Gray/Black
Right Front Speaker Wire (+): Red/Green
Right Front Speaker Wire (-): Brown/Black
Rear Speakers Size and Location: 6′ x 9′ Rear Deck
Left Rear Speaker Wire (+): Blue/Yellow
Left Rear Speaker Wire (-): Gray/White
Right Rear Speaker Wire (+): Red/Yellow

You don't want to fit that - it's the factory amplifier for the rear speakers (the rears are amped, the fronts are not). You need to run new wires from the head unit back to the new rear speakers so that the speaker-level outputs from the new head unit are used to drive the new speakers.