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PAC AmpPRO AP4-FD21 Aftermarket Amplifier Interface

Allows seamless addition of an amplifier in select 2012-up Ford vehicles

Item # 541AP4FD21

You can make a less-than-ideal  factory system actually sound premium by upgrading the weak factory amplifier...

Find what Fits your vehicle

You can make a less-than-ideal  factory system actually sound premium by upgrading the weak factory amplifier...

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Item # 541AP4FD21

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About the PAC AmpPRO AP4-FD21 Aftermarket Amplifier Interface

Buck Pomerantz

Your amp will sound better than the factory system

You can make a less-than-ideal  factory system actually sound premium by upgrading the weak factory amplifier with a more powerful aftermarket amp. PAC's AmpPRO interface consists of a module and a vehicle-specific T-harness that make the job much easier. Now, you can install an amplifier of your own without losing any of your vehicle's factory audio features like warning chimes, navigation prompts, and Bluetooth functions.

Your amp will sound better than the factory system

You can make a less-than-ideal  factory system actually sound premium by upgrading the weak factory amplifier with a more powerful aftermarket amp. PAC's AmpPRO interface consists of a module and a vehicle-specific T-harness that make the job much easier. Now, you can install an amplifier of your own without losing any of your vehicle's factory audio features like warning chimes, navigation prompts, and Bluetooth functions.

Simple to install

The package's T-harness plugs into the factory radio and vehicle harness. The small module fits behind the dash, converting your radio's speaker outputs into six preamp-level outputs ready for connection to your amp. The factory amplifier needs to be left connected in the vehicle. The factory radio controls, such as volume, balance, and fade, will work as before for your front and rear speakers. A separate wired remote level control lets you adjust the volume of the subwoofer channels from your front seat. An optional add-on module, PAC's APA-TOS1 adapter, provides an optical digital output for your high-end digital processors and amplifiers to handle.

An app for tweakers

After downloading the AmpPRO PC App and connecting to your Windows-run PC via USB, you can access the factory 3-band parametric equalizer (EQ) and customize the tone of your system to perfection. The app also lets you adjust chime volume, the system's minimum volume level, and update the product firmware when needed.

Important Note: This AmpPRO interface simplifies the installation of a car amplifier (not included). You'll also need to purchase anything required to install your new amp: an amp wiring kitspeaker wire (to replace factory wiring), and RCA cables.


Product highlights:

  • amplifier integration module and T-harness
    • add an aftermarket amplifier without removing factory amp
  • works with select 2012-up Ford vehicles
  • 6-channel RCA outputs (front, rear, subs)
  • switchable 5- or 4-volt RMS output
  • retains factory radio controls and audio features
  • wired remote level control for sub channels
  • remote turn-on lead for amplifiers
  • AmpPRO PC App, available from PAC, lets you adjust minimum and chime volumes and 3-band EQ via your Windows-run PC
  • optional TOSLINK adapter provides digital output
  • warranty: 1 year
  • Our 60-day money-back guarantee
  • MFR # AP4-FD21

What's in the box:

  • Amplifier integration interface module
  • T-harness
  • 6' Rotary-knob cable
  • Rotary-knob
  • Installation Instructions

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<< >>

More details on the PAC AmpPRO AP4-FD21 Aftermarket Amplifier Interface

Stacey B.

Product Research


Amplifier Integration Interface: The PAC AmpPRO AP4-FD21 simplifies the installation of aftermarket amplifiers in select Ford vehicles with data-bus controlled factory sound systems. With the AmpPRO AP4-FD21, you can improve your vehicle's audio performance while keeping an original radio's fit, finish, and features.


  • The factory radio and factory amplifier must remain connected in the vehicle and be operational in order to use the PAC AmpPRO interface.
  • If you are only using the PAC AmpPRO interface to add a subwoofer amplifier, the factory amplifier will still power the other speakers in the vehicle.

Vehicle Compatibility: The PAC AmpPRO AP4-FD21 amplifier integration interface is compatible with the following 2013-2020 Ford vehicles with a data-bus controlled factory premium sound system.

Make Model Year
Ford Edge 2015-2017
Escape 2016
Expedition 2015-2017
Explorer 2011-2018
F- 150 2013-2017
F-250/350/450/550 2013-2019
Focus 2012-2017
Fusion 2013-2016
Mustang 2019-2020
Taurus 2013-2015
Note: 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. If this brand is not shown, check for the presence of a center speaker or subwoofer.

6Ch Pre-Outs: The PAC AmpPRO AP4-FD21 provides a 6-channel pre-amp output for use with aftermarket amplifiers. Using the full-range, fixed level factory radio output, in conjunction with data-bus CAN messages, the AP4-FD21 delivers a variable 5V RMS pre-amp output with fading, balance, equalization, and level control capabilities.

Non-Fading Level Control Knob: Channels 5-6 (Sub) of the AP4-FD21 are non-fading outputs. The output level of channels 5-6 can be controlled using the supplied level control knob. The level control knob comes with a 6' cable which plugs into the interface module and should be mounted in an accessible location.

Data Controlled Remote Turn-On: A data controlled remote amplifier turn on wire is also provided by the PAC AmpPRO AP4-FD21. The remote turn-on is rated at 2A of current. If more current is needed an external relay must be used.

Retained Factory Audio Features: The PAC AmpPRO AP4-FD21 also retains all audio from other vehicle features such as factory Navigation Prompts, Bluetooth, Sync, and Warning Chimes.

Minimum & Chime Volume: If the minimum volume of your factory radio is too loud once the AP4-FD21 is installed, you can manually set the level of the minimum volume using either the programming button on the side of the interface or the factory SWC (Steering Wheel Controls) in conjunction with the supplied level control knob. You can also use AmpPRO PC app. You can also adjust the chime volume level.

AmpPRO PC App: Using the AmpPRO PC App (for Windows PC only) allows you to configure user interface options such as Minimum Volume Level, Chime Volume Level, and a 3-Band EQ from your Windows computer or laptop. The app can also be used to update product firmware.

  • Minimum & Chime Volume Level: From the app you can set the minimum volume level of the factory radio, as well as the chime volume level.
  • 3-Band EQ: Enables the 3-band EQ (Bass-Mid-Treble) with frequency and Q-factory adjustment. The Bass Frequency can be set to 60, 80, 100, or 120Hz; while the Bass Q-Factor can be set to 0.5, 1.0, 1.5, or 2.0. The Mid Frequency can be set to 500, 1k, 1.5k, or 2.5k; while the Mid Q-Factor can be set to 0.75, 1.0, 1.25, or 1.5. The Treble Frequency can be set to 7.5k, 10k, 12.5k, or 15k; while the Treble Q-Factory can be set to 0.75 or 1.25.
  • Firmware: The AmpPRO app will also allow you to update the interface with new firmware as it becomes available.
Note: These AmpPRO PC App settings can be adjusted with the module installed in the vehicle or on the bench. However, it is recommended to make the adjustments with the module installed, and the factory radio on so that the changes can be heard.

Dip Switch: Set dip switch 2 to "ON" to lower the RCA output voltage to 4V. Set the dip switch 2 "OFF" to keep the RCA output voltage at 5V. Dip switches 3-4 are used for troubleshooting Sync & Bluetooth. Dip switch 1 is not used.

Optional Toslink Add-On Module: When used in conjunction with PAC's APA-TOS1 (541APATOS1; sold separately), the AP4-FD21 can provide a variable 2-channel fiber optic digital audio output (toslink). Toslink fiber-optical cable also sold separately.

Optional Amplifier Harness: The APH-FD01 installation harness (541APHFD01, sold separately) simplifies speaker wire connections when using the PAC AmpPRO AP4-FD21 (sold separately) to add an aftermarket amplifier or amplifiers in select 2007-2017 Ford and Lincoln vehicles that feature factory amplified sound systems. The APH-FD01 keeps you from having to cut or modify your vehicle's original factory wiring, providing a direct connection at the vehicle's original factory amplifier location (you will need to make hardwire connections at the aftermarket amplifier/s). 

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Customer Q&A

20 questions already asked

The AP4-FD21 unit came with a 10 pin TOSLink socket, not the 12 pin socket that the APA-TOS1 kit expects per the installation instructions. The left-most 2 pins hang loose outside the socket on the circuit board. Will this still work when I install it?
[ AARON  Nov 17, 2022 ]
1 answer
Greetings Aaron, and thank you for your question. It sounds like you need some technical support for your PAC AmpPRO. We do offer that for our customers. If you purchased that from Crutchfield, you will have a direct to tech number on your shipping email confirmation. If you purchased this elsewhere, you should be able to get the needed support thru PAC by calling 727-592-5991.
[ Thomas  Nov 17, 2022 ]  Staff
If I have an aftermarket radio in my 2012 F150 with factory navigation Sony system, will I need this PAC module to run an aftermarket mono amp and subwoofer? I'm just looking to replace the factory subwoofer but keep everything else powered by the factory amp.
[ LUIS  Oct 19, 2022 ]
1 answer
Greetings Louis, and thank you for your question. You would only need the PAC AmpPro interface if you were keeping the factory radio, and adding amplifiers to that radio. If you have an aftermarket stereo, use the subwoofer RCA out jacks and run those to your subwoofer amplifier.
[ Thomas  Oct 19, 2022 ]  Staff
will this work on a 2018 Ford Fusion with a factory amp with 8inch screen?
[ elvin  Dec 21, 2021 ]
2 answers
Amp pro web site should tell you. It should, it depends on what they are trying to do with it.
[ MIKE  Dec 21, 2021 ]
It works in my 19 Ford F-250 with factor 8 inch so it should in yours
[ ANDREW  Dec 21, 2021 ]
Does this come with the optical module or do I need to purchase that separately?
[ ZACH  Nov 23, 2021 ]
3 answers
You need to purchase separately
[ MICHAEL  Nov 25, 2021 ]
Have to purchase separately. Awesome piece of equipment
[ JASON  Nov 24, 2021 ]
I purchased about a year ago and the optical module must be purchased separately. You have to take the AP4-FD2 cover off, snap in the optical module purchased separately and then re-assemble. Easy to do.
[ JUSTIN  Nov 23, 2021 ]
Pac-audio says this is compatible with my 2014 Ford Taurus (Limited) with 8" screen and Sony system. However, your site says it is not. Why is this?
[ James  Jun 15, 2021 ]
1 answer
We were not aware this would work in the Taurus' which is why we didn't list it. We had our research team check the compatibility and update our systems. Our site should update within 24 hours of this reply and show this AmpPro interface when a compatible 2013-2015 Taurus has been entered into our vehicle fit guide.
[ JASON  Jun 29, 2021 ]  Staff
Can two aftermarket amplifiers be added with this harness? I want to use a 4 channel for door speakers and a monoblock for subwoofer and keep the factory head unit.
[ Dylan  Apr 06, 2021 ]
2 answers
Yes you can. There are RCA outputs for Front, Rear and Sub. You could also use RCA splitter if you needed to do more or you could use a processor to achieve what you want to do.
[ JUSTIN  Apr 06, 2021 ]
Yes either use the two sets of RCA's for the 4 channel amp and the last set for the monoblock. Or if you want to go the digital optical out route then get the add-on and just run one optical with the signal wire back to the dsp/amp and you're good to go.
[ GRANT  Apr 06, 2021 ]
Will this work on a 2019 F-150 with the 8" display, 7 speaker non B&O stereo?
[ Don  Apr 17, 2020 ]
2 answers
I wouldnt tap into rear speakers for a sub. I used this in my ford 1 ton to add a sub. It works pretty good! No splicing, RCA jacks on module. I unplugged factory sub when i was done.
[ MIKE  Dec 21, 2021 ]
It should, it's a waste of money. If you are trying to hook up a sub amp to the system tap into the rear speakers and install a line out converter and save the money. $20 compared to $300
[ CHRIS  Apr 17, 2020 ]
If i install one of these in my 2012 PLatinumber F150 will i need to install a 4 channel amp at the same time or will the factory amp and head unit still provide sound to the speakers while i wait for a 4 channel? Biggest thing im looking to add is a subwoofer package first so a 4 channel is down the road. But i will do it all at once if needed
[ dizzle  Mar 25, 2020 ]
3 answers
factory amp still works with the speakers till you unplug it from the main amp. I would recommend if you plan on doing both, that I would at least either run two sets or rca's or your digital optical or whatever your preference is and the same with running your signal wire so you do not have to take the stereo back out. Hope this helps.
[ GRANT  Apr 20, 2020 ]
Yes when installed the factory stereo will remain working. The only thing it changes is the factory EQ settings to flat. Also you will be surprised as to how much bass put out your factory sub will now have.
[ CHRIS  Apr 20, 2020 ]
The beauty of this device is that you can install and continue to use your factory system until you are ready to switch over to your aftermarket speakers. This device just grabs the signals, but does not cut them off, so your factory system still works.
[ JUSTIN  Apr 20, 2020 ]
Trying to see if this is compatible with my 2018 Taurus SHO. It has the "premium" sony package that needs upgraded. There are other model years of the same generation Taurus (13-15) that fit but the 2018 is not listed. I would like to try it but what would the return policy be if it didn't work?
[ Matthew  Aug 31, 2019 ]
1 answer
We can't confirm that PAC harness will work based on our research file on the 2018 Taurus and the information provided in the PAC manual. You are welcome to give it a try - -we have a 60 day return policy if it does not work. I would suggest instead this Rockford Fosgate DSR1 in combination with an iDatalink t-harness:
[ CASEY  Sep 11, 2019 ]  Staff
Is there a solution to the added noise that is introduced by the module?
[ JACKSON  Jul 27, 2019 ]
2 answers
Mine didn't make any noise that I could tell. I ran a jl audio hd600.4 and it sounded great.
[ RAYMOND  Jul 30, 2019 ]
Optical module
[ Cone Computer  Jul 27, 2019 ]
Will the Toslink connection allow me to connect my Audio control DM810 DSP and still use all output channels on the DSP? The details say the toslink only provides 2 channels of signal?
[ JEREMY  Dec 12, 2018 ]
4 answers
Yes - you can connect the Toslink output of the AmpPro to your DM810 and the DM810 will split the 2 full range channels into 4 full range pairs and one mono pair for your subwoofer. It will also give you level controls between each channel in the PC interface.
[ CARL  Dec 12, 2018 ]
Yes, you can use all your output channels. The DSP software processes and routes the signal to the DSP outputs. The optical signal the Amppro puts out is a non fading pure stereo PCM signal. I am using all 8 channels of my JL Audio Twk-D8 DSP with the optical output from the Amppro feeding it.
[ CHAD  Dec 12, 2018 ]
That's technically a question which pertains to your DSP, not this PAC adapter. For example, using my JL Audio TWK-D8 I can take the 2 channels (full range) from the PAC AmpPro and map or route those to any combination of EQs and crossovers within the DSP. With 2ch stereo input I can get all 8 channels out of my DSP in any combination I need. Go get super comfy with your DSP documentation and/or software and you'll find your answer.
[ Anthony  Dec 12, 2018 ]
Yes all of the output can be used. What I believe you lose is the ability to fade front to rear since the toslink only provides stereo left and right.
[ Patrick Van  Dec 12, 2018 ]
The manufacturers website says the compatibility is for up to a 2017 F-150. Has anyone gotten this to work in a 2018?
[ JEFFERY  Jul 16, 2018 ]
1 answer
If you have the Sony system this will work. If you have the B&O system you need the Nav-Tv
[ Cone Computer  Jul 17, 2018 ]
Why won't this fit a 2010 with factory Sony sound?
[ Kyle  Dec 17, 2017 ]
2 answers
You didn't mention the model of you vehicle but...I believe you should look into PAC AmpPro mode# AP4-FD11. You may have better luck.
[ Anthony  Dec 12, 2018 ]
I checked but we didn't get any information as to why this product doesn't work in a 2010. I'd guess its either the connection, the audio transfer method, or maybe both. You might be able to call PAC to see if they have specifics on this product. Their phone number is 800-336-6500. My Bio:
[ JASON  Dec 21, 2017 ]  Staff
when will you stock the AP4-FD11? (the one for a 2011 F150 with the Siny system)
[ B  Dec 15, 2017 ]
1 answer
I don't see this product anywhere in our databases right now and cannot find any information on if we will even carry it. I did put in a request to our merchandising team to pick it up. Hopefully we will! My Bio:
[ JASON  Dec 31, 2017 ]  Staff
Will this work to supply RCA outs in a 2015 f150 8" with MyFordTouch that has the base sound system (not Sony)?
[ JOSEPH  Nov 27, 2017 ]
2 answers
Short answer, no, this will not work for you. The PAC site states clearly that these interfaces require the amplified/premium OEM Sony sound systems. The reason is that these interfaces sit between the factory amplifier (absent in your system) and the factory stereo interface, and interpret the communications between them.
[ Anthony  Dec 12, 2018 ]
I don't know as my truck had the Sony system, which it worked fine with.
[ Marc  Nov 30, 2017 ]
Can I retain factory speaker wires?
[ FOUAD  Aug 23, 2017 ]
2 answers
If you look on Pac-Audios site they offer a module that plugs into the factory plug and you can wire it directly into an amp without cutting factory wires.
[ Cone Computer  Jul 17, 2018 ]
The PAC AmpPRO simply provides the RCA pre-amp outputs you'll need to provide audio to an aftermarket amplifier. When adding a high-powered amp, I definitely recommend running thicker, aftermarket speaker wire to ensure the full power and fidelity from the new amp makes it to the new speakers.
[ Ryan  Aug 26, 2017 ]  Staff

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