Back up your original GP3.EXE . Then copy the modded GP3.EXE (which includes the season calendar) into the root folder. This is where most users fail—they try to use the old .exe with new car files.
Copy the modded CARS , TRACKS , and GRAPHICS folders, allowing overwrites. grand prix 3 mods work
However, if you are looking for a "one-click install" experience like modern Steam Workshop mods, GP3 will disappoint you. The mods work, but you have to make them work through manual file management. Back up your original GP3
Install GP3 + Patch 1.13 in a non- Program Files folder (e.g., C:\Games\GP3 ). Windows UAC blocks mod writing. and GRAPHICS folders