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Scosche C4MA02 Wiring Interface

Allows you to connect a new car stereo and retain the Bose® audio system in select 1993-up Mazda vehicles

Item #: 142C4MA02

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34 Reviews | 1 question - 1 answer

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The Scosche C4MA02 wiring interface allows you to integrate a high-powered aftermarket receiver into select 1993-up Mazda vehicles with premium factory systems. The package includes the OEA-4 adapter and a Mazda-specific harness. The OEA-4 unit has output-level gain controls for each of its four channels which can be adjusted to properly match the new receiver to the factory amplifier.

Note: If you haven't already, please enter your vehicle information or call a Sales Advisor at 1-888-955-6000 to find out if this adapter is compatible with your vehicle.

  • 4 speaker-level inputs
  • output level adjustments for all four channels
  • works best with high-powered aftermarket receivers
  • dimensions: 3-15/16"W x 15/16"H x 2-1/16"D
  • 1-year warranty

Note: Most vehicles will require additional installation parts — please identify your vehicle if you haven’t done so. You can also call an Advisor for more information.

Scosche C4MA02 Wiring Interface Reviews

Average Customer Review:

34 Reviews

Worked well

Written by: Doug G from Pennsylvania on November 30, 2015

2000 Mazda Miata
Crutchfield Customer Review (What's this?)

I used this to adapt a kenwood stereo to my 2000 Miata Bose stereo and it worked as advertised.



Scosche C4MA02 Wiring Interface

Written by: Anonymous from Illinois on October 19, 2015

2001 Mazda Miata
Crutchfield Customer Review (What's this?)

I found the supporting documents to lack information needed to use the product with my Miata as expected. I ended up having to buy more product in order to complete my project which in turn left me using only part of the product.

Pros: Long wires, hard plastic

Cons: lack of information in supporting document

Good, but no necessary with new head units that have a additional volu

Written by: Ekisela from Ft Walton, Florida on September 21, 2015

2001 Mazda Miata
Crutchfield Customer Review (What's this?)

The adapters a nice piece if you have an older head unit. For the unit that I watered, this adapter was not needed as it has a supplemental volume control. Please perform research as to What units require this adapter. All in on easy way to install a new unit to the Bose system.

Pros: Pros are universal adaptability from any aftermarket head unit to the factory Bose system and Ease of installation. An easy way to install a new unit to the Bose system.

Cons: Cons are your selected head unit may have a supplemental volume controls to attenuate the signal going to the Bose amp. Please perform research.

Great product!

Written by: David from Alabama on August 7, 2015

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

The Bose head unit in my 99 Miata went out, and the only way to use the stock speakers is with this harness thing, it's not to complicated, and now I have a new radio that actually works!

Pros: Works with no adjusting the dials. They were just all balanced center

Cons: It's not model specific, my car only has front speakers so some of the wires aren't used which can be confusing if you don't do your research.

Scosche C4MA02 Wiring Interface

Written by: Anonymous from New Jersey on June 9, 2015

1993 Mazda RX7
Crutchfield Customer Review (What's this?)

Installed in a 1993 Mazda R-7 with factory BOSE system. Does not work out of the box. The factory amps were not turned on by the relay. There was no pin in the connector in the correct location. Relocated un-used pin from the other connector to get it working.



Scosche C4MA02 Wiring Interface in 99 Mazda Miata with Bose

Written by: Scosche C4MA02 in 99 Miata with Bose system from New York on June 2, 2015

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

Gotta have it, check the Miata forum for info to provide needed connection for Green & Black pre-amp wire, the parts are there you just need a paper clip and use an additional left over wire.

Pros: It is pretty straight forward, don't get hung up on the colors of the wires in the dash harness not matching the scosche harness.

Cons: Wow, don't look at the colors of the wires in the dash connector, just add a wire to the scosche harness to mate up with the Green & Black wire of the car audio harness for the Bose pre-amp.

Works great - 1999 Miata

Written by: JS from Massachusetts on May 18, 2015

Crutchfield Customer Review (What's this?)

Google "Keep your Bose Speakers and Replace Head Unit: a How To" you'll be glad you did. After an easy modification to the Scosche harness, there is no need to splice into the Amp harness. Turned down the L/R Rear speaker as there are none, set the L/R front to the mid-point. Plugged it in, turned it on, sounded great.

Pros: Sounds great, keeps the factory Bose amp and speakers

Cons: If you take the time to modify the Scosche harness, there are no cons.

Makes for an easy installation

Written by: DarrenR from White Rock, BC on April 27, 2015

2000 Mazda Miata
Crutchfield Customer Review (What's this?)

Made for a perfect install with a couple of minor modifications

Pros: Creates a perfect connections to the stock stereo

Cons: Require a few modifications to the wiring harness to get all connections working.

It Works with modification

Written by: Thaejor from California on April 26, 2015

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

4 stars because you pretty much need this to install an aftermarket head and retain use of the Bose amp. On my '99 miata, I had to do some counterintuitive splicing behind the stock harness, but it does the job.

Pros: Lets you keep the Bose system

Cons: Almost certainly requires a call to Crutchfield tech support

Scosche C4MA02 Wiring Interface

Written by: Anders from New York on April 21, 2015

Crutchfield Customer Review (What's this?)

Terrific high quality product which made installation a smooth and stress free process on my 1999 Miata! As usual, Crutchfield Customer Service was courteous, professional and helpful!



An appropriate interface

Written by: RonE from California on April 6, 2015

2001 Mazda Miata
Crutchfield Customer Review (What's this?)

Installing a 'normal' receiver in a car that has non-standard sound hardware (a separate amplifier and 'special' speakers) requires having an interface between the receiver and the amplifier that presents that amplifier with appropriate inputs. This interface provides not only that capability; but the ability to adjust the input levels to the amp so it is not overdriven, and has the right levels to make best use of the amplifier's dynamic range. The Scosche interface performs well in this role, and was reasonably easy to incorporate into the wiring harness.

Pros: features, clear instructions, performance


Works Great On 1999 Mazda Miata

Written by: Jay from Round Rock,Texas on April 5, 2015

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

I installed a Pioneer FH-X700BT in my '99 Mazda Miata with Bose and It was a little confusing at first but thanks to customer support I got this working perfect.

Pros: Easy once figured out. Good customer support.

Cons: "Manual" is confusing.

Scosche C4MA02 Wiring Interface

Written by: Chuck from The "D" on March 14, 2015

2000 Mazda Miata
Crutchfield Customer Review (What's this?)

incomplete instructions, found correct wiring on Miata site, if instructions were correct a higher rating would have been given.

Pros: It works after some rework

Cons: poor instructions,

Too many wires, bad instructions

Written by: Charlie from Florida on February 15, 2015

2000 Mazda Miata
Crutchfield Customer Review (What's this?)

I ;purchased a Kenwood KDC-BT558U for my 2000 Mazda Miata MX5 and the recommended additional material needed for installation to my Miata Bose power amplifier. As is turned out the this wiring harness was sent to me for adapting to my vehicle was for front and rear speakers. Mazda Miata only have front speakers for this year. Direction with this unit sucked. I had to call Crutchfield tech services twice. Both time the Technician at Crutchfield walked thru it with me. First I no power. Second I had no sound. The second call the tech told me that I had to splice a wire that was behind the vehicle harness and spice a wire from there to the receiver wiring and it worked.

Pros: Wrong interface for 2000 Mazda Miata. Wiring instructions sucked. After two calls to technical support interface worked.

Cons: Crutchfield Tech center GREAT

The answer to my prayers!

Written by: ScottG from New Mexico on January 27, 2015

2000 Mazda 626
Crutchfield Customer Review (What's this?)

This device was tough to figure out, because its job is so weird -- it steps down the impedence (or power, I don't know which!) from the head unit so that it doesn't blow the 2 ohm Bose speakers that came with my Mazda (most car stereo speakers are 4 ohm). The coloring of the factory wires can be unique to each car model (in older cars, at least).

I connected the Scosche by following the diagram, but no joy. Scosche tech support was all I could have hoped for. It took the guy awhile to research, but he was able to determine that the problem was a diiferent-colored wire that brought power to the amp (located under the passenger seat). Once I connected the wire he indicated, it worked great.

This was just the kind of tech support experience we all hope for, but rarely get -- a real person answered the phone and was actualy able to helped me!

Pros:  Price  It works  Tech support

Cons:  None

Scosche C4MA02

Written by: Dean from Sedona, AZ on January 27, 2015

2000 Mazda Miata
Crutchfield Customer Review (What's this?)

The interface works fine and was easy to install. However, one of the splices connecting the interface to my vehicle's connectors had come apart inside the packaging, and 2 others were loose. So I repaired all the connections with solder and shrink-tube.

Pros: Good product

Cons: Poor workmanship


Written by: John from Blairsville Ga on October 19, 2014

2001 Mazda Miata
Crutchfield Customer Review (What's this?)

Went in easy !!

Pros: Works well

Cons: cant find any

Scosche wiring interface

Written by: DonB from Naples, FL on September 27, 2014

I was buying a Pioneer AVIC-8000NEX radio at another supplier but I was using your recommendations for additional material needed for installation to my Miata Bose power amplifier. As is turned out the Pioneer radio had all the adjustments needed for adjusting preamp levels to the Bose amplifier, but I left the Scosche interface with attenuation adjustments in at zero attenuation because I did not want to rewire after I had the radio working and installed. Your recommendations for this item to go with a Pioneer AVIC-8000NEX radio is incorrect . For people that don't install radios but once in a great while, they don't know what is needed and take your recommendation as true and necessary.

Pros: It worked as it was supposed to.

Cons: For me, since it was put in a Miata 2 seater, I did not need the rear speaker capability and there was a lot of unnecessary wiring. The product worked as it was supposed to but the low rating is because of Cruchfield not knowing the capabilities of the radio that I was looking at.

Crutchfield response on October 7, 2014 Don is correct that in this case, he only needs the front channels since his Miata doesn't have rear speakers. And even when the gain controls are set at their lowest settings, as in this case, the Scosche adapter is still doing its job. It's slightly attenuating the stereo's signal, making the Pioneer stereo a better match for the car's Bose system. Whenever you're shopping for car audio gear, don't hesitate to contact our advisors via phone, email, or chat. They can answer questions about stuff like this before you buy and make sure you get exactly what you need.

Still need to modify

Written by: JC from San Francisco, CA on August 12, 2014

Crutchfield Customer Review (What's this?)

I can't believe Scosche can market this as a customized item for a Miata with Bose. First of all, you don't need the rear wires since the miata only has front speakers, so you can chop those off. The big thing here is that the power to the amplifier pin is completely wrong. I chose to modify the harness pins (with one of the extra wires i chopped off) so I could keep the install clean using the wiring harness (no messing with the bose harnness). Search 'Keep your Bose Speakers and Replace Head Unit' on Miata's website to see what I'm referring. Luckily, my head unit came with a separate pin for the power antenna, otherwise you'd have to use the same amp power pin (you can add a switch if you don't want the antenna up all the time when the radio is on).

Pros: It clips in to stock bose adapter? Sound quality good. Adjustment is simple. When the adapter is properly modified, it makes for a clean installation.

Cons: Still need to modify.

As described

Written by: TurboRX from Gig harbor wa on May 2, 2014

Crutchfield Customer Review (What's this?)

Just what I needed to convert bose acoustic wave head unit to a new head unit. The adapter enabled me to still utilize the bose speakers which have an individual amplifier for each speaker. The local installers were unable to figure out the wiring so I put them on the phone with Crutchfield tech support. Problem resolved within minutes. Too bad there is not a Crutchfield store in Gig Harbor to perform installs.

Pros: Thank goodness for Crutchfield

Cons: None

Scosche review

Written by: GrayDD from Alvin, Texas on December 31, 2013

2000 Mazda Miata
Crutchfield Customer Review (What's this?)

Used to connect a Kenwood system to an existing factory Bose speaker system in my Miata. Over all pleased with the outcome however the instructions for installation were severely lacking and a call to tech support was required. Tech support was fantastic and had me squared away in minutes.

Pros: Sound quality was awesome and adjustable features were just what was needed.

Cons: Installation instructions were not good to say the least. (was not plug and play) had to cut and splice into the factory wiring, which is exactly what I did not want to do. Kind of defeated the purpose of buying a plug and play adapter. Was not that big of deal as tech support got me on target right away.

easy to install, but not complete

Written by: JasonF from Atlanta, GA on June 2, 2013

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

Worked great to add a JVC head unit to my miata, but had to change a pin to make the amp work... and if it is made for a miata, I only need two channels (If it could've been smaller), real estate in the dash is rather tight. But wiring it to the JVC harness was simple and quick. It made installation simple!

Pros: color coded, easy to use

Cons: could've been a two channel model, and prewired for the amp on/off - if I could adapt it so easily, why not just offer a version?

Scosche adapter

Written by: Dave E from Grass valley, CA on May 20, 2013

Crutchfield Customer Review (What's this?)

The reason for the "two stars" only has to do with the workmanship on the product. The wire splices made by the manufacture were terrible. The crimps were loose and one was completely detached. I first called Crutchfield to get a replacement, but was told it would take another week plus to get the replacement. The tech at Crutchfield was not the most helpful personal. He told me "me just sell these we don't make them!". I chose to keep the bad unit and repair it my self. I cut out all the splices and redid the connections with solder. The unit work well, once repaired, and I can say I am happy with it. Just be prepared to fix this product if you should order it.

Pros: Works after repair

Cons: very poor quality control on workmanship.

Missing a pin

Written by: Turborascal from Austin, TX on July 23, 2012

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

Somewhat bulky, this unit does the intended job after moving a pin to power the factory Bose amp with unit powered-up. I'm disappointed that Scosche fails to provide separate pin-outs to independently trigger the power antenna and power amplifier. If following their instructions, the antenna would go up whenever the head unit is on, rather than with the tuner only. Fortunately, this was installed in a Miata that lacks rear speakers. Speaking with Crutchfield tech support provided the correct factory harness pin to trigger the power amp. Moving a pin/wire from an unused rear speaker position to the correct location allows the head unit to turn the amp on without having the antenna rise; while the antenna rises when the tuner is selected. This product needs to provide connections for all permutations of factory equipment without the need for modification. That said; it works once modified.

Pros: Does the intended job.

Cons: Bulky, fails to provide separate trigger pins/wires for power antenna and power amplifier. Must be modified to properly work with both.

Works fine - needs update to work for the Miata

Written by: Nick P from Minneapolis, MN on May 22, 2012

Overall, this unit works as intended. As others have said, it's not plug-n-play -- you need to splice some wires to connect to the Bose amp. The tech support at Scosche found the issue on the first call and was able to remedy it.

I wish the wires were longer so that I could relocate the adaptor to the glove box. As is, it's tucked behind the double-din head unit, which makes any adjustments very diffficult.

Pros: Works great

Cons: Poor instructions. Short wires mean adjustments after install are very difficult.

Works like a charm

Written by: JayBee from Charlotte, NC on September 16, 2011

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

I was putting a Kenwood KDC-X595 head unit in a 1999 Mazda Miata with the factory Bose system. The integration with the Base system forced some adaptations, and the Scosche worked like a charm after installation. I was replacing a double DIN unit with a single DIN unit, so I had lots of room. That meant it wasn't at all difficult to dial in the settings which you must do with the radio in operation. If the placement was tighter, it might have been much more challenging. My only suggestion -- make the wires long enough so the Scosche unit can reside permanently in the glovebox and easily be reached for tuning after buttoning up the installation, instead of putting it behind the head unit where it is now unreachable until the end of time.



Missing amp power lead

Written by: Badbob 19919 from Seattlle Wa on September 3, 2011

Crutchfield Customer Review (What's this?)

Product works great except theres a missing pin for the amp power so had to do some splicing. Also product kinda big ,didnt really need a 4 channel ,2 ch would have been 1/2 the size.Thought about cutting it in half



99 Mazda Bose System Patch

Written by: Scott S from Seattle Wa on June 29, 2011

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

This device scales the output of the main deck befre going into the inputs of another source. In my case I chose to keep the Bose speakers and amplifier that came with the 99 MX5. I cut off the harness for the rear speakers since there none in the MX5. The only issue was the power lead for the Bose amp was missing. I had to take one from the connector I cut off and insert. Then it worked great.



Worked, but not without modification.

Written by: Scott B from Austin, TX on May 23, 2011

The Scosche adapter did not include a connection the the power-control wire that activates the factory installed Bose amplifier. It took several phone calls, and it was Crutchfield service that finally came up with the solution.

I had to remove the control wire from the factory harness and connect it to the P.CONT wire of my Kenwood receiver.

Not that this was extremely difficult to do, but it is a significant oversite on the part of this adaptor to leave that wire in the harness without a companion wire in the adaptor plug. Add to that no instructions on this wire and the fact that Scosche had trouble diagnosing why I had no sound in my speakers, and I have to give this product an unacceptable rating.



Product Great, Instructions lacking one key thing...

Written by: David W from Nashville, TN on May 22, 2011

2000 Mazda Miata
Crutchfield Customer Review (What's this?)

2000 Miata SE w/ Bose AM/FM/Cassette replaced w/Pioneer Double-DIN unit

Product performs as described, box is big to hide in the dash, but creative stuffing makes it all fit. Would be nice if they offered a 2-channel version seeing as I cut the rear cables to make room. One big issue, this harness did not provide a pin for the Bose Amp "on" sensor. As described by the other reviewers, we needed to add, splice or weld a connection from the radio to the Bose amp switch (so the amp would turn on when you turned your new head unit on.) This was not in the instructions (very un-Crutchfield like.) You guys have spoiled me in the past with flawless step-by-step instructions. This time there was a "gap."

A little searching on the miata-dot-net forum provided a description and pictures on how to add the "amp on" wire. When you buy this product, search for this topic "Keep your Bose Speakers and Replace Head Unit" and you'll be set!



It works, but it took some fiddling

Written by: Paul G from San Jose, CA on March 7, 2011

2000 Mazda Miata
Crutchfield Customer Review (What's this?)

I got the setup for a Mazda Miata with Bose amplifier. It works quite well,
once it's installed, but it took some fiddling with the help of the Miata online
forum to get the wiring harness right. That being said, Crutchfield's service
support was quite good, and the tech rep was able to confirm what wire needed to
be rerouted.



more information - less calling

Written by: Anonymous from Pittsburgh. PA on August 7, 2010

2001 Mazda Miata
Crutchfield Customer Review (What's this?)

After 4 calls to the vendor for technical support, which could have been spelled out in the minimal instillation information page provided. This adapter works, I guess, fine because the radio purchased and installed at the same time sounds great.

Just an installers note: If you want not to have the power antenna in the up position all the time, place a small switch inline on the power antenna sense wire, when your using the AM/FM throw the switch, when your using the CD/AUX port turn it off as it originally would do in the OEM radio. This was installed in a '01 Mazda Miata SE with the Bose Stereo system.



Scosche C4MA02 Wiring Interface

Written by: Marlin from N.E. Ohio on October 3, 2008

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

I bought this adapter for my Miata. It works fine, and the install is almost dummjy proof. The only problem is that there is not a power wire for the Bose amp inb the car. Since my radio doesn't have a dimmer feature, I just relocated the dimmer wire to the amp feed location. Viola! Works like a champ. I can even drown out the wind noise with the top down!



Hey it works but could be better

Written by: Brian from New Jersey on May 10, 2006

1999 Mazda Miata
Crutchfield Customer Review (What's this?)

The Good:
This item will allow you to keep your bose amp working in a miata because it can transpose an amp'ed signal to a line level out put. The item in the picture is exactly what you get.
The Bad:
This item is not designed for the miata. It is designed for a car with four channels of audio. It is called a four channel car because it has component tweeters with built in crossovers (which are located in the door). So as you can see in the picture there is an adapter coming off the main conector which has two green and two purple wires, these are the rear channels. This entire connector and wires are completely useless-left floating in the consol. Further the bose amp needs to tap into the 12 volt aux power wire to power the bose amp. (or you get no sound) This wire is the little mint green 22AWG. it connects to the factory harness but this item does not connect to it. there is an empty hole where they should have put another wire. The only way you can tap into this power is to put a 'pinch' and crimp into that little wire (not easy since its in the center of the cluster). There are other wires my install left with no use too. But those are the main issues. If you have a two channel system like a miata, don't get this item. There are similar two channel devices out there. This item is based on the Ven 4 (4 channel model) the Ven 2 is all you need.

If you are installing Alpine IVA-D310 you don't even need a line level adapter. The D310 RCA line level output for amps.



Hands-on research

What's in the box?

Download owner's manual

  • OEA-4 OEM Amp interface (with 8-wire input with bare wires/8-wire output with 2 white rectangular connectors)
  • Flat-blade screwdriver (attached to interface module)
  • 13 Crimp caps
  • Instruction sheet

Product Research


Compatibility: The OEA-4 (model C4MA02) is a non-electronic interface that allows an aftermarket high-power stereo to integrate into select 1993-up Mazda vehicles with Bose premium factory systems. Please check the Crutchfield Vehicle Selector for compatibility for your vehicle.

Adjustment Gain Controls: Four rotary gain controls (front left, front right, rear left, rear right) are located recessed inside the adapter chassis. There is a small flat-blade screwdriver attached to the adapter's case, and its use is recommended. The controls are very fragile and sensitive, and a slight adjustment will change volume dramatically.

Harnesses: The adapter's input wires are approximately 5-1/2" long with bare ends. These splice to the new receiver's speaker output wires. The adapter's output wires are approximately 11" long and terminate into two white rectangular Molex plugs. There are 4 additional wires coming from one of the white plugs that should be spliced to the receiver's wiring harness. The Molex plug ends are molded to match with the factory wiring harnesses. Crimp caps are provided for wire splices.

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team. They verify what’s in the box, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.

Customer Q&A

1 question already asked

For details on fit or installation please contact an Advisor by phone (1-800-324-9695) or online chat. They will be able to pull up your vehicle and give you the details on if this will fit and what you will need for an installation in your vehicle. [ Krissy  Aug 10, 2014 ]  Staff

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