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The complete(ish) guide to installing an aftermarket stereo in the MG3


In this guide I’ll try and give you a detailed account of how I undertook my own installation. I don’t claim to be correct in every regard but what I’ve done seems to work for me and has done for a couple of months. This is not a complete step-by-step guide intended for beginners. If you’re going to use this information you will need to have a good working knowledge of car audio and electrics.

The techniques and methods I’ve used have had budget, aesthetics and reversibility taken into account. In my case I was just looking for better fidelity. I’m not about to go down to the local boy-racer’s meetup on the sea front to try and lift skirts with bass. Just some more control over the sound.

Every part of the system can be put back exactly to how it was before. No permanent modifications have been made to the car. This is useful if ever a warranty claim needs to be made. All modifications can be undone or hidden before the car goes back to the dealership, or when I decide to sell the car on.

The modifications I’ve done are:

  • Replaced the factory head unit.
  • Added a subwoofer.
  • Installed a dash cam.
  • Integrated the steering wheel controls.
  • Integrated the factory microphone.
  • Integrated the factory DAB antenna.

I ended up keeping the factory speakers in the doors and A pillars because they sound just fine after adding a bit of EQ.

I’m not using the Aux input and USB connector in the top storage compartment. I have both of these connectors available on the front of the new head unit so there was no need to wire them in separately.

There is a parts list at the end of this post.

Head Unit

The head unit I’m using is a Kenwood KDC-X7000DAB. I picked this up on an Amazon Warehouse clearance deal for about £80. It’s nothing particularly amazing but it does everything I need it to do and sounds alright.

The most challenging part of the job is getting the factory head unit out of the dash board. For this you will need a set of radio removal keys (linked in the parts list). They need to be inserted into the two small slots on the face of the radio and pulled outwards, away from each other. The head unit can then be carefully pulled out of the dash. See the photos below for a better description. The last photo shows the radio out of the dash with the tip of the key engaging the spring clip that locks it in place.

Luckily the factory head unit, despite external appearances is a standard single DIN size and uses mostly standard wiring and connectors. The power (A), speaker (B), and miscellaneous (C) connectors are standard ISO 10487. The FM antenna is on a standard “Motorola” style connector.

Pinout for the speaker connector is completely standard. Pinout for the power connector is standard apart form the permanent and ignition power lines (red and yellow on a standard loom) being swapped. The misc (C) connector is completely non-standard and took a bit of work to figure out. More on this later.

If all you’re interested in is sticking a basic head unit in and not bothering with the mic or the steering wheel controls then you don’t need to worry about the misc connector. Your new radio should come with a loom to go between the car’s wiring and your new head unit. Just plug in the power and speaker connectors (with your permanent and ignition lines swapped!) and off you go.

Finally I used an adapter fascia plate to fill the hole surrounding the new head unit.


I installed a Vibe OptiSound Auto 8 active under seat subwoofer. Because I was going for reversible-ness I didn’t want to run wiring all the way to the boot of the car. Plus I get to keep the boot space. Also, a smaller sub like this has far more reasonable power needs. No need to run thick cabling from the battery in the engine bay.

While I had the head unit out of the dash board I ran the signal and switch-on lines inside the dashboard behind the glove box, then down the bottom of the A pillar and along the passenger door sill. The pop out from under the trim underneath the passenger seat.

Removing the glovebox is pretty straightforward. Open it up, press in hard in the spot where the stop hits the inside of the dashboard and push the stop past it’s usual limit. Do the same for both sides, then just pull the whole thing towards the passenger seat to unclip the hinges.

I cable tied the lines onto the metal bar that should be clearly visible in front of you. You’ll need to run the lines along the back of the bar so they don’t get in the way of the glovebox opening and closing.

Next is the bottom of the A pillar and door sill. Remove the bonnet release handle by prying it off with a flat-head screwdriver wrapped in a rag. Remove the screw located near the passenger’s left foot. Pull up the door seal around the bottom of the door then carefully pull the trim panel off. This should give you a clear path to the area under the passenger seat.

For power I used a breakout fuse to take power from the fuse box in the passenger foot well. I used a 10A fuse from Halfords plugged into the rear wiper timer fuse location. I figured that this is a fairly non-critical circuit if it does go wrong, and the group of fuses that this one is in is fed from fairly high capacity circuit that doesn’t have many other heavy loads on it.

Make sure when you install the breakout fuse that the breakout wire is facing towards the rear of the car so that power is being taken from the un-fused side. The wiring supplied with the subwoofer has an inline 20A fuse which will need to be wired onto the breakout wire as close to the fuse as possible.

The sub is fixed to the carpet under the seat with two strips of velcro. I’m using the “hook” side glued onto the bottom of the sub with contact adhesive.

Dash Cam

The dash cam I’m using is a basic unit from Amazon. I won’t recommend a particular model because they all do much the same thing and work in much the same way. The available selection seems to change week by week.

Basically all I’m doing here is taking a 5V USB power feed from the back of the Kenwood head unit. There are kits available to take a 12v feed and drop it down to 5v. This would be wired into something like the ignition line on the back of the head unit if yours doesn’t have a USB connector on the back. As with the sub, the wiring runs along the metal bar behind the glove box, then up into the A pillar.

The A pillar trim is removed by pulling off the door seal then carefully pulling the trim piece off, starting at the top. The uppermost clip is different to the others. It will only come off a short distance at first. You’ll need to reach behind and detach a small tether from the trim piece so you can pull it off completely. I suspect this is something to do with the curtain air bag.

While you’re in there be careful of this strip of fabric. I don’t know exactly what it is or what it’s for but it’s probably part of the curtain air bag. Best to leave it well alone.

Finally the cable can just be tucked in along the gap between the roof liner and the windscreen glass, then dropped down wherever you fancy putting the camera.

Steering Wheel Controls

This is where it gets interesting! This bit is specific to Kenwood and possibly JVC head units but I can’t guarantee it’ll work with anything but the head unit I’ve used.

Kenwood do sell adapter boxes to integrate various manufacturer’s controls into the head unit. They don’t sell one for this car though.

After a lot of poking around I found that the controls appear on pins 5 and 6 of the misc connector. 5 is ground and 6 is the signal line. The resistance between these two wires varies depending on which button on the steering wheel is pressed.

I used an Arduino Nano to translate these resistance values into a digital signal that the head unit can understand. I can share the code and a circuit diagram if anyone interested. Actually building it will take some skill and isn’t something I’d recommend as a My-First-Soldering-Project.

Maybe I’ll turn this section into a separate thread because it’s far too much detail to put here as part of another topic.


The mic for the call audio is in the ceiling next to the dome light. The also appears on the misc connector behind the head unit on pins 8 and 9. Pin 8 is signal and pin 9 is ground.

I made up a loom using a male ISO 10487 C connector block to adapt this to the 3.5mm jack connector on the back of the Kenwood head unit. The factory mic does have some circuitry in it which takes power from the head unit over the cable. The Kenwood head unit seems to work with it just fine though this is down to chance as much as anything else. Again, I don’t guarantee that this will work with any other head unit.

DAB Antenna

For the first few weeks of running this setup I was using a film antenna stuck to the inside of the windscreen. This didn’t get the best reception nor did it look great. To be fair to the factory system the DAB reception was always great unless I was really in the middle of nowhere.

The factory antenna is part of the FM antenna on the roof of the car. The antenna has a built-in signal booster which is powered by the head unit. The factory head unit doesn’t actually have a DAB receiver in it. This is done by a separate module which takes the signal from the antenna, decodes it and feeds it into the head unit as an analogue signal.

The DAB antenna is plugged into the DAB module which is located inside the dash by the passenger foot well. To get to it, undo the plastic clip and pull the trim piece away.

The antenna connector is the green “Fakra E” connector going into the side of the module. Disconnect this and use a Fakra E to SMB adapter lead to connect it to the head unit.
Again, I make no guarantees that this will work with any other head unit other than the one I’ve used. Mine appears to supply the correct power to the signal booster for it to work correctly. Also, different head units use different connectors for the DAB antenna feed.

The adapter lead I used is a bit short at 50cm. With it plugged in at the module end it’s too short to plug into the Kenwood head unit. I have to plug everything into the back of the head unit, push it into the dash then plug the far end of the adapter lead into the car wiring down at the DAB module.

Parts List

Head unit



DAB antenna


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I wonder why on MG 3 remote controls from steering wheel were put on lins 5 and 6 when usual "standard" is to put them on pins 11 and 12. I know that manufacturers tend to use their way of putting things, but some industrial "standard" makes people expect things at certain place and because of that can accept cars better.

What are the resistance values from MG 3 remote controls? I wonder this in accordance to change of pins as mentioned above.

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That’s an excellent writeup. The standard unit in my wife’s 3 leaves a lot to be desired, FM is ok, DAB works when it feels like it and the clock has a mind of its own. I’d thought about replacing it but assumed it would be a strange shape and as she wasn’t complaining left well alone. She’s also asked about getting a dash cam fitted and although I hadn’t tried too hard to find the fuse box it wasn’t immediately obvious where it was.

You say “I used an adapter fascia plate to fill the hole” I haven’t looked for one as I assumed they wouldn’t be available, where did you get this?

If I go down this route I may come back to you about the Arduino code, I’ve used Nano’s and Digisparks for a number of projects.

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Discussion Starter · #6 ·
I wonder why on MG 3 remote controls from steering wheel were put on lins 5 and 6 when usual "standard" is to put them on pins 11 and 12. I know that manufacturers tend to use their way of putting things, but some industrial "standard" makes people expect things at certain place and because of that can accept cars better.

What are the resistance values from MG 3 remote controls? I wonder this in accordance to change of pins as mentioned above.
Who knows what our SAIC overlords were thinking.

Anyway the resistance values are:
* 61.4k for no buttons pressed
* Vol Up is 740ohm
* Vol Down is 2.73k
* Skip >> is 5.41k
* Skip << is 9.68k

Thr factory head unit uses a 10k resistor internally and a 5v supply to make a voltage divider.

I calculated the voltage values for each button press and they matched up pretty closely with measurements.

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I'd like to put the Alpine Halo 9 in mine but can't justify the £700 price tag.
I don't like the MG sat nag setup as that looks too much like an afterthought and seems to be pretty rubbish.

The Saudi Market (I think it is anyway) aftermarket system looks better but again cost and reliability is a worry.

The only other way I can see a solution is a single din motorised screen or some sort of tablet install.

Nice to see what you have got done on yours though and with a bit of work anything is certainly possible.

Sent from my AGS-W09 using Tapatalk

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I know im late to the game but just wanted to let ppl know incartec sell a kit for these which has everything needed to install aftermarket stereo and retain mic, dab steering controls plus fascia. Not cheap think i paid £86 posted. Pretty much plug and play. Also worth mentioning the Sony DSX-A410bt 55wx4 is a perfect match with the dash clocks red/white. Can be had for reasonable money and makes the factory speakers sound way better. I believe £99 at Halfords. It doesn't have dab though. I am also considering a vibe optisound auto 8 and wondering if anybody thinks they are worth the money.
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