Open Definition Setup


We will be using only one type of application, a compression utility.

Below is a few links for a utility, we only need one. I will be using WinRAR.

Windows 10+ Users: You most likely have a built-in compression utility within Windows you can use for these steps. We will NOT be packaging a mod in any of these steps and only need the ability to extract or unpack an archive to a folder. So you can skip to the next section if you prefer to use the built-in utility,

Portable vs Install

Most applications or programs have an option to download a portable or installer version. We will make a few points on each before we choose which version to select. I run an installed version of WinRAR.

Portable: For minor tasks and minimal usage a portable version is a simple lightweight option you can run from a USB stick or random folder location. You simply execute the application, complete your task and done. When you have repeated tasks or use the program regularly you are missing out on the benefits of the installed version. It is advised to use an installed version if you plan to regularly pack and edit mods. Another benefit of the portable version is it makes zero changes to your registry or file system.

Installer: An installer will generally have benefits like right click menus, the ability to create one click operations and saving default methods just to name a few. An installer will also usually make changes to the registry and create configuration files on your pc like any other application, this may or may not be a drawback for you. You must uninstall the program if it is not wanted anymore vs deleting the folder you run a portable version from.

Download & Install

Choose your preferred application and download. Follow the steps to install or run from the creator.

If you are using something other than WinRAR, now would be a good time to learn how to use or for the purpose of this guide, extract the contents of an archive. Most archivers will let you drag and drop vs using a built-in utility.


We need to decide where we want to work on our open definition pack. We can go ahead and create a folder anywhere you like, but there is a lot of unnecessary steps that come with that, such as copying or transferring contents to mod folder and/or packaging modified files back into an archive with the proper settings.

It is better to create a folder in your American Truck Simulator – mod folder. This will let us make changes and edits, reload a profile in game and check our changes without repackaging or restarting the game.

From now on when I refer to your Open Def or Open Definition, I will be talking about this folder we will be creating in the next step. When I reference the archived or packed version I will explicitly mention that, as in iw900_opendef_v1.0.scs archive.


We will start by creating a new folder in your American Truck Sim mod folder.

You can name this anything you like, it is only for you to identify the folder.

The display name and mod icon will be taken care of by the mod manifest.

Select the open def archive you would like to edit. You can choose a trailer or truck or both.

I will do the IW900 Open Def, so I select and open the iw900_opendef_vx.x.scs archive.

I now open the new folder we created in our mod folder and extract, move or drag and drop the contents of the iw900_opendef_vx.x.scs archive into this folder.

If you cannot see all the files after extraction and/or copying you can refresh your display on windows by right click>refresh.

Right click > Refresh

Info and Changelog

Inside the open def you have a readme file, this has basic info and mod load order along with some template info.

Mod load order images are also available inside the open def.


Templates for skinning paintjobs and decals are located in the ‘UV_MAPS’ folder.


Images for saving your templates and decals to are located in the ‘decals’ folder.

All other relevant or needed locations will be discussed in detail in the proper guide. From here you can edit and change files and accessories for your mod.

If you mess up or have crashing just follow the steps below, or from the start of this guide to get a fresh open def to edit again.

Mod Manager

Open the mod manager and verify the package name from mod info.

We then replace the original Open Def with our modified version.

Load the game and ignore all warnings of a missing mod.

This warning will be from our original open def mod being replaced.

If you have made changes that cannot be reversed or undone, you have two options.

  • Delete and extract a new open def archive
  • Extract and replace broken or missing files.

To start fresh with a new open def, just delete the contents of the open def folder you created and have edited in. Then follow the steps above to extract a new archive to your folder.

To replace a bad, missing or broken file we obviously need to know which file and the location of it. Then we can open the open def archive (iw900_opendef_vx.x.scs) and replace the files we need to by extracting or dragging and dropping the clean new files into the proper location. We can choose to replace the files or delete the affected files and start with fresh ones.

See example below for replacement method with WinRAR.

Here we replace messed up license plate image files from the open def archive.

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