Mark Houlahan
Tech Editor, Mustang Monthly
January 2, 2018

Our Week to Wicked Mustang hit the 2017 SEMA Show floor last November to much fanfare. Every time we stopped back in our booth there was a large crowd around the Mustang, and it was also well received going through the SEMA Ignited parade on Friday night. All in all we feel the project has been a huge success. So much so that we’re planning a second Week to Wicked classic Mustang build for later this year, so stay tuned for more details on the what, where, and when of that happening.

One of the last post-build week projects we needed to complete to wrap our Week to Wicked Mustang was adding some serious audio to our 1966 hardtop. With the Mustangs to Fear custom door panels we installed wearing their Kenwood component speakers, we were itching to get some sound to them. Couple that with California’s hands-free driving laws for phone use—we wanted to step up to something with Bluetooth capability to stay safe and legal. Lastly, we wanted our audio source to be able to handle multiple inputs and fit the classic Mustang dash without cutting. We found the solution to all these needs and more with a direct-fit head unit from Custom Autosound.

Custom Autosound offers several direct-fit stereos, and we fell in love with its latest piece of tech, the USA-740. The USA-740 offers a classic/retro look but with a digital tuning faceplate packed with features like RCA pre-outs for amplifiers; Bluetooth audio and phone streaming; USB input for phone or media player connectivity (or just a thumb drive of your favorite driving music!); auxiliary inputs for satellite radio; and even RDS tuning that displays the song and artist.

The USA-740 packs plenty of punch all on its own, but we paired the unit with Custom Autosound’s famous “Backseat Driver” module. The Backseat Driver system incorporates an 800-watt amp and two 8-inch subwoofers into a vehicle-specific mounting board for easy installation. The Mustang Backseat Driver fits ’65-’69 Mustang hardtops, and everything is pre-wired. Simply connect the amp’s power and ground leads and provide the amp with a turn-on signal and input from the head unit.

Lastly, while we had our pre-installed door speakers pre-mounted in our Mustangs to Fear door panels, we wanted to add a little more to the setup for proper front and rear staging with a dual voice coil dash speaker and a pair of traditional 6x9s in the package tray. The dual voice coil speaker is designed to be a direct-fit replacement (in the case of the ’66 it is a 4x10-sized speaker) for the original mono speaker in your dash, yet that provides increased bass response while accepting both the left and right stereo inputs from your stereo.

We dug into our Week to Wicked Mustang over the course of a sunny California afternoon upon our return from the 2017 SEMA Show (driving it home via historic Route 66 no less!) and had our system up and thumping before dinnertime. Installation is nut-and-bolt simple with hand tools and just the basics for wiring (switched power, constant power, ground, and your speaker connections). You’ll be glad you did this install once you hit the road—we sure are!

1. The Custom Autosound USA-740 comes out of the box ready to install (knobs mounted for photo, but they are included loose). The wiring harness uses industry standard power/speaker colors, and the Bluetooth microphone and auxiliary input cable are included too.
2. The Backseat Driver is a great way to increase the bass output in your Mustang hardtop with a very simple installation. There’s no confusing wiring or trying to cut a piece of wood to mount your amp and speakers; it’s all done for you in advance.
3. The dual voice coil 4x10 dash speaker might seem like a trivial add-on when you have two 8-inch subwoofers and a set of component speakers in the doors (or kick panels), but this little beast belts out some great sound, and is an easy addition to the speaker wiring.
4. There are several options for removing the old radio. If you have the factory Ford radio, it is quite big and will require removal from under the dash or from the glovebox. Older aftermarket radios are usually small enough to come out the top, through the dash opening for the 4x10 speaker. We’re removing the gauge cluster regardless so we have access to wiring and to support the radio during installation.
5. Two screws secure the speaker/defroster grille on the ’65-’66 Mustang. Once the screws are out, lift up to remove. Our 4x10 speaker was long gone, but if yours is still in place, remove the retaining screws to extract it as well.
6. Remove the old radio’s knobs and retaining nuts/washers. If the factory rear radio brace is still installed, then that needs to be removed as well (from the radio and the top of the dash).
7. Because the radio we were removing was an ancient Custom Autosound cassette deck, it was small enough to remove from the top. Disconnect the wiring plugs for power and speaker(s) before extracting the unit. As we mentioned earlier, you might have to remove your glovebox insert or temporarily move your underdash A/C unit to one side for radio removal.
8. Having a Painless Performance wiring harness in our Week to Wicked Mustang made wiring easy, as the Painless chassis harness kit includes both switched and constant power wires for radio installation. If you have factory wiring you can find switched power at the ignition switch (or original radio wiring), and we recommend the cigar lighter for the constant power connection for radio memory and settings.
9. We decided to handle the speaker wires for our Mustangs to Fear door panel–mounted component set first. This would be similar for the very popular kick panel speaker options out there as well. Route a length of speaker wire from the speaker location to the center of the dash area, noting location (LF, etc.). We then did the same for our rear deck-mounted 6x9 speakers.
10. Next, we mounted the Backseat Driver. We’ve seen this unit mounted from the trunk and from the back seat–side of the package tray area, and we prefer mounting it from the interior. Either way, it fits very snuggly in place.
11. Another shot, but from inside. We added some self-tapping screws at the bottom to secure the panel, and we’ve started to route the wiring to the front of the car. Always route your power wire separate from any signal/speaker wires.
12. The pre-installed ground lead simply takes a ring terminal, and is secured to the adjacent metal structure with a tapping screw once the metal has been sanded clean.
13. The amplifier’s power lead is routed directly to the battery. Since we have an Old Air Products A/C system installed, we were able to easily route the power lead through the old heater hose opening in the firewall; however, if you don’t have such options you’ll need to route the wire through a new hole, and don’t forget to protect the wire with a rubber grommet.
14. The remaining amp wiring includes the blue amp turn-on lead and the RCA pre-out wires. We routed these up the driver side of the car, opposite the power lead and to the center of the dash for connecting to the radio harness. The radio has two blue wires, one for an amp and one for a power antenna, so be sure you’re connecting the amp turn-on lead to the proper one.
15. If equipped like our USA-740, the USB cable will need to be routed to an easily accessible location. We chose the glovebox by simply passing it through the opening in the insert in the upper corner. Other options include the ashtray or forward storage bin of a non-A/C “long” console.
16. Installing 6x9 rear deck speakers is a bit of a challenge in the early Mustang like the ’65-’66, as the deck only had one center-mounted speaker (which was a rare option at that). To properly install 6x9 speakers requires some trimming of the factory package tray metal, or even cutting it out completely and installing a flat sheet of metal with the speaker cutouts.
17. With the package tray modified appropriately, the new 6x9 speakers can be installed from the top (through the fiber package tray trim cover) and secured. Ensure the speaker wiring is zip-tied or otherwise secured to the bottom of the package tray so items placed in the trunk do not catch and damage/disconnect the speaker wires.
18. With all the wiring in place we highly recommend connecting all of the wiring for the speakers, amp and radio power, etc., and “bench testing” the system before installing the new stereo. This gives you a chance to double-check wiring and that sound is coming from all speakers before you button up the interior too. Everything worked perfectly on our setup, so it was time for final installation.
19. The new Custom Autosound stereo mounts from the back of the dash just like the old/original radio. Secure it to the dash with the included washers and nuts (just a bit more than snug is all you need). Be sure to either use the original rear support bracket, adjusted to fit, or utilize the universal bracket/strap material included in the Custom Autosound box to support the radio’s weight. Install the reproduction knobs and reinstall any removed trim/panels/etc. and you’re good to go.
20. While not shown earlier during our wiring phase, the included microphone is connected to the rear of the stereo and must be routed so it can pick up the driver’s voice. We recommend mounting the microphone either at the base of the steering column in front of the speedometer or at the top of the driver-side A-pillar near the headliner.