Sunday, May 5, 2024

Replace Head Unit in an MX-5 NC2 (2011) - 3. Wiring Diagrams

Car / MX-5 / Radio.

When possible I try to understand what I'm doing, and why. That doesn't always work out 😏 but at least I try 😁

This is my first radio install in... well... thirty years? So I grabbed all the diagrams I could find, and tried to understand when I needed SWCs and LOCs, and when not.


SWC Adapter

1. If your car uses a CAN bus for the SWC then you typically need a SWC adapter. In the MX-5 the CAN bus isn't used for the radio, so it just depends on the new head unit.

2. If you use a brand name unit you may have to offer it a voltage, or specific resistances, or certain levels, in which case you need an SWC controller. If your new head unit is a Chinese Android box they can typically 'learn' the different levels and most of the time you won't need an SWC adapter.

See also here.


LOC or CTAMPPASSTHROUGH

This is a level converter that is only required if your car has a Bose unit installed AND you use the speaker-outs of your new head unit. In that case the signals are too high and need to be lowered.

See also here.


Diagrams

I collected information on ISO connectors, the Mazda radio connector, and (in my case) the Atoto unit.

If you use another brand or model of head unit then you'll have to check what wiring it requires, but this information may help you to figure things out.


I used the Atoto -> Bose diagram at the bottom, with a CTAMPPASSTHROUGH module, and it works fine. Note that I only needed those ISO connectors because I used a CTAMPPASSTHROUGH module.


    Selected images

    (The file is an Excel sheet with images and additional information. Download it for more details.)


    Mazda Radio connector


    (Click any image to enlarge.)


    ISO connector


    A modified ACV harness (for a Pioneer head unit with a Bose amplifier)

    I bought an ACV harness from Cabriohoeve, but in the end didn't use anything except for the CTAMPPASSTHROUGH unit. And I plan to replace that one with a DIY version later.

    Below is the wiring diagram using an ISO harness as provided by Atoto, combined with the ACV harness, and a few additional wires. You should be able to compare this with any other head unit and adapt accordingly.


    The CTAMPPASSTHROUGH unit

    An alternative to the typical transformer based LOC:




    Atoto to MX-5 radio connector with a CTAMPPASSTHROUGH

    You can simply leave out and replace the CTAMPPASSTHROUGH module with either a DIY alternative, or a LOC.

    You should be able to adapt this to any Chinese Android head unit. Note: some units might need an SWC adapter, though most don't. Mine worked fine without.


    (Click on any image to enlarge.)


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