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 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 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.