This is my first Add-on car. Everything works fine, but I could not find way to make my tuning parts working. After lot of time waste spending in attempts, I finally decided to set mod kit to "0_default_modkit". That way car at least has some modifications.
Anyway I included all tuning parts in the .dlc file, so if you are an expert you may want to try to make it working. Please let me know if you make it, i would like to learn it too.
You can choose between two versions of the car (plates shape)

1.Copy "2011mazda2" folder to :\Grand Theft Auto V\mods\update\x64\dlcpacks

2. Using OpenIV, go to: \Grand Theft Auto V\\mods\update\update.rpf\common\data — find the "dlclist.xml"
and add the following line:

dlcpacks:\2011mazda2\
dlc_2011mazda2:/
update:/dlc_patch/2011mazda2/



Done!

To spawn the car using the trainer type:
2011mazda2