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 © 2017 AAMP Global. All rights reserved. PAC is a Power Brand of AAMP Global.

PAC-audio.com

Pacific Accessory Corporation

Page 1

Rev. 053017

Advanced Amplifier Interface 

for Ford 

AP4-FD21

The AP4-FD21 provides a 6-channel pre-amp output for use with aftermarket audio equipment. Using the full range, 

fixed level head unit output, in conjunction with CAN messages, the AP4-FD21 delivers a variable 5v RMS pre-amp 

output with fading, balance, equalization, and level control capabilities. The module also retains all audio from other 

vehicle features such as factory Navigation Prompts, Bluetooth, SYNC, and parking sensor chimes. 

A data controlled 

remote amplifier turn on wire is also provided by the AP4-FD21. When used in conjunction with the APA-TOS1 (sold 

separately), the module can provide a variable 2-channel fiber optic digital audio output (TOSLINK).

Introduction and Features

Important Notes

1.  This interface is only compatible in vehicles equipped with a data bus controlled premium sound system. To verify 

compatibility, look for a Sony badge on the door speakers, center speaker, or factory sub woofer. 

2. 

The factory amplifier must remain connected, and in the vehicle after the AmpPRO has been installed.

3. 

The remote output is rated at 2A of current. If more current is needed an external relay must be used.

4.  The remote output may remain active once the key has been removed if the vehicle needs to pass chime or SYNC audio.

5.  If your chimes played through the factory speakers, and all speakers have been disconnected from the factory amp, all 

chimes will then play through the speaker in the dash.

6.  Channels 5 and 6 are non-fading outputs. The output level of channels 5 and 6 can be controlled using the supplied level 

control knob.

7.  The chime volume and minimum volume levels are set to 0 dB by default. If you are happy with this level in your particular 

application then additional adjustment is not required. Please refer to the Setup and Configuration section on page 2 for 

more details.

8.  Ford Focus:

 You cannot use the steering wheel controls to activate the chime and minimum volume adjustment.

9.  The level control knob must be connected in order to manually adjust the chime volume and minimum volume settings.

10. 

The factory radio's speed controlled volume and surround sound mode are not supported by the AP4 outputs.

11.  No adjustments can be made manually using the programming button, or the factory SWC when the module is connected to 

a PC.

Wiring Connection Chart

To Aftermarket

Amplifier

Non-Fading

Rear

Front

1(L) 2(R)

4(R) 5(L) 6(R)

3(L)

Remote Turn On Output

2A Max Output

To Vehicle

Harness

To Radio

To LCD 

Screen

Non-Fading

Level Control 

Knob

To Vehicle

Harness

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