What is carcols.meta?

The root element is CVehicleModelInfoVarGlobal. The base game's own carcols file also defines the global paint colour list, but the version shipped with an add-on vehicle normally contains only the blocks that car needs:

• Kits: mod kits. Each has a kitName, a numeric id, a list of visibleMods (parts with their own model) and statMods (performance upgrades such as engine, brakes and transmission).
• Sirens: siren settings for emergency vehicles, each with an id, that define timing and flash patterns for the siren lights on the model.
• Lights: light settings, each with an id, that define the colour and intensity of headlights, tail lights and indicators.

<CVehicleModelInfoVarGlobal>
  <Kits>
    <Item>
      <kitName>1234_mycar_modkit</kitName>
      <id value="1234" />
      <kitType>MKT_SPORT</kitType>
      <visibleMods>
        <Item>
          <modelName>mycar_spoiler1</modelName>
          <modShopLabel>MYCAR_SPL1</modShopLabel>
          <linkedModels />
          <turnOffBones />
          <type>VMT_SPOILER</type>
          <bone>chassis</bone>
          <collisionBone>chassis</collisionBone>
        </Item>
      </visibleMods>
      <statMods>
        <!-- engine, brakes, gearbox, armour ... -->
      </statMods>
    </Item>
  </Kits>
</CVehicleModelInfoVarGlobal>

Each modelName under visibleMods is a separate .yft in the stream folder, here mycar_spoiler1.yft. modShopLabel is a text label key for the part's name in the mod shop.

carcols.meta never mentions the vehicle directly. carvariations.meta makes the connection: its kits list names the kit by kitName, and its sirenSettings and lightSettings values hold the numeric IDs of the entries to use. A kit that is defined but not referenced there does nothing.

files {
    'data/carcols.meta',
    'data/carvariations.meta',
}

data_file 'CARCOLS_FILE' 'data/carcols.meta'
data_file 'VEHICLE_VARIATION_FILE' 'data/carvariations.meta'

Kit, siren and light IDs are global across everything the client has loaded. Mod authors pick IDs independently, so two cars from different authors can easily use the same number. When that happens, one definition wins and the other car gets the wrong data.

• No tuning parts, or another car's parts, in the mod shop: two kits share an id. Give one a number no other resource uses, and keep the number at the start of kitName in step with it by convention.
• Tuning parts listed but invisible: the part .yft files are missing from the stream folder or named differently from modelName.
• Emergency lights flash in the wrong pattern or not at all: two siren settings share an id, or sirenSettings in carvariations.meta points at the wrong one.
• File has no effect at all: the CARCOLS_FILE data_file line is missing.

Checking IDs by hand across a large server is tedious. The Car Pack Builder reports kit ID conflicts when it merges vehicles into one resource.