Keeping the radio on after the engine shuts off

The Mazda MX-5 (ND) has one annoying issue. As soon as you shut off the engine,  the Radio/Bluetooth system immediately turns off. This is especially annoying when you are on a call, but have to stop the car in a parking lot or garage. Most other car radios will continue working until you open the door to exit.

There is a little trick for the AT version. If you press the button on the shifter and turn off the engine at the same time, the radio will stay on. I published this finding on the Miata forum, but this is not a solution for cars with MT.

To resolve this issue, I decided to design a little device – controller, which will keep the ACC relay on until there is a CAN message indicating the driver’s door is opening.


As shown on the wiring diagram above, the ACC relay is controlled by START STOP UNIT (SSU) pin 2C (yellow wire). This wire needs to be cut, to allow mixing control with an additional device.

To make the installation process easier and to avoid cutting the yellow wire, I designed a plug-n-play harness for SSU 24 pin connector.



The 24 pin connector on SSU beside ACC control wire has wires for HS-CAN, Battery power, Ground – which is all I need for my controller.


Now, after the engine is off, my device will supply the power to keep the ACC relay on. CAN bus will notify when the driver opens the door, and it will signal to turn off the ACC relay. In addition, there is 15 minutes timer which will turn the relay off, even if you’re still in the car. This is to avoid deep battery discharge. The controller will go into deep sleep mode and will wake up on new CAN activity.


In addition, this same device can be used  as an alternative to my Warning Timer for Turn Signal.


ACC-ON Installation Instruction (rev 1.0)

Available here.

Update 7/31/2019:

Recently successfully tested in Mazda CX-5 2016, with minor harness modification.

Available here

Installation is much easier due to better access to connectors.



26 thoughts on “Keeping the radio on after the engine shuts off

  1. Just a heads up: All plug and play remote start systems use a t-harness and connect to the start-stop unit. All of the instructions for these units come with a strong caution to disconnect the battery prior to installation. Messing with the start-stop unit without first disconnecting the battery can somehow burn up the keyless entry module elsewhere in the vehicle.


  2. Any eta on what day these might be available? I’ve been wanting this since day 1 and this’ll be the perfect reason to grab a few other things from your store.

    Super appreciative of all the support you’ve been adding to our vehicles.


  3. I installed mine today. It works great. Thanks! On the 2019 with tilt steering wheel, I used a 12” screwdriver through the opening with my left hand to open the connector’s tab and then reached under to pull it loose. Then, again through the front opening attached the new harness. It was all pretty easy from this position. I couldn’t get either loose while laying under the dash. Perhaps 2019 is different because of the tilt wheel? But you can look in and see both connectors


  4. Installed this about a week ago. Works great just as expected.

    Two items for possible improvement, not that it needs improvement….
    1) When the engine is turned off and the ACC still has power, you need to press the on button twice to get back to the ON (all the dash lights on) position.
    2) When the engine is turned off and the ACC still has power, when you open the door, the car alert chimes twice and the left display shows Engine On warning.

    Once again these are MINOR items and well worth no accidentally dropping a Bluetooth call or listing to the end of a great song without leaving the engine running.


    • “2) When the engine is turned off and the ACC still has power, when you open the door, the car alert chimes twice and the left display shows Engine On warning.” this is not happening in 2016 MX-5. Maybe Ignition mode was on without starting engine?


  5. Hey gang… installed the mod without a problem. But now when I push the clutch in, the start button is not green. It flashes amber. What did I do wrong? How do I fix? Thx.


  6. Apologies in advance if I missed this in the description. What happens if you decide to turn it back on? I am thinking of quick stop scenario, stopped on backroad for a few minutes waiting for entry to a one-lane section (often happens on my back roads), I sometimes am torn between turning the engine off and having to go through the infotainment/android auto reset.


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  9. Hello,
    how does the acc/IG power controller works BEFORE entering the car?
    If the acc/ig controller is installed, will my Ignition always been turned on when i unlock the car?
    asking for the roof controller.


    • Without an RFC controller, it will not do anything. With RFC installed, it will turn on Ignition for 30 seconds on the second or third click (as defined by configuration software)


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