Newbie help: Aftermarket head unit for '99 Audi A4

[hornakapopolis]

My only previous experience has been swapping out head units that had already replaced factory units, so I've never had to deal with this wiring/amp issue before. This is probably has an easy solution if you know what you're doing.

I have a '99 Audi A4 with the regular (non-Bose) stereo. I'm using an old Pioneer DEH-X66BT receiver and bought a "VW Lead to Car Harness 94-80" (VW-9000) wiring adapter from Best Buy.

I matched all of my colors and was left with the blue wire from the receiver with a blue sticker over the tip saying "System Remote Control" and, from the car, a dark orange cable with a white stripe, thicker than the majority of the other wires I connected.

Everything works but the rear speakers. I swapped the front speakers wires from the receiver to the back speaker wires and they still do not work.

I keep running across a mention of an amp connection that's supposed to send power to an amp that would activate the rear speakers, but when I run across mention of it, there's either no response regarding what connection to use or the response is saying that it doesn't apply to the factory install. There's certainly no after-market amp of any kind in this car.

There are four (or two) connectors that were connected to the factory stereo that are not connected to anything at all, if it matters. 3 small light blue, green, and yellow connectors, connected together and a large red connector.

I appreciate any help anyone can give me.

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[keep_hope_alive Premium Member]

if you can look at the rear speakers, you can identify wire colors. then look for those in the harness that isn't used.

i didn't find a 1999 A4 but found colors for a 2000 A4

2000 Audi A4 Car Stereo Radio Wiring Diagram

Car Radio Constant 12v+ Wire: Red/White

Car Radio Switched 12v+ Wire: Black/Blue

Car Radio Ground Wire: Brown

Car Radio Illumination Wire: Gray/Blue

Car Stereo Dimmer Wire: N/A

Car Stereo Antenna Trigger: N/A

Car Stereo Amp Trigger Wire: N/A

Car Stereo Amplifier Location: N/A

Front Speakers Size: N/A

Front Speakers Location: N/A

Left Front Speaker Positive Wire (+): Blue/White

Left Front Speaker Negative Wire (-): Brown/White

Right Front Speaker Positive Wire (+): Red

Right Front Speaker Negative Wire (-): Brown/Red

Rear Speakers Size: N/A

Rear Speakers Location: N/A

Left Rear Speaker Positive Wire (+): Brown/White

Left Rear Speaker Negative Wire (-): Blue/White

Right Rear Speaker Positive Wire (+): Brown/Red

Right Rear Speaker Negative Wire (-): Red

another option is to just bypass stock wiring and run new wiring from the new HU to the speaker directly.

 

[macsdad 10+ year member]

if you can look at the rear speakers, you can identify wire colors. then look for those in the harness that isn't used.
i didn't find a 1999 A4 but found colors for a 2000 A4

2000 Audi A4 Car Stereo Radio Wiring Diagram

Car Radio Constant 12v+ Wire: Red/White

Car Radio Switched 12v+ Wire: Black/Blue

Car Radio Ground Wire: Brown

Car Radio Illumination Wire: Gray/Blue

Car Stereo Dimmer Wire: N/A

Car Stereo Antenna Trigger: N/A

Car Stereo Amp Trigger Wire: N/A

Car Stereo Amplifier Location: N/A

Front Speakers Size: N/A

Front Speakers Location: N/A

Left Front Speaker Positive Wire (+): Blue/White

Left Front Speaker Negative Wire (-): Brown/White

Right Front Speaker Positive Wire (+): Red

Right Front Speaker Negative Wire (-): Brown/Red

Rear Speakers Size: N/A

Rear Speakers Location: N/A

Left Rear Speaker Positive Wire (+): Brown/White

Left Rear Speaker Negative Wire (-): Blue/White

Right Rear Speaker Positive Wire (+): Brown/Red

Right Rear Speaker Negative Wire (-): Red

another option is to just bypass stock wiring and run new wiring from the new HU to the speaker directly.

Nice to see actual help, as opposed to, why did you buy that schit instead of this schit, or that's what google is for.