@samanthajones020 There are two different places Sims 3 files are going to land. The program files should be installed on D, which is what Origin is supposed to be doing. These are the files that make the game run, and we're not supposed to mess with them or add anything there. (Mods were placed in program files when the game was originally releaseed, but the mods setup changed more than eight years ago.)
The Sims 3 game folder lands in Documents\Electronic Arts, wherever Documents is located on your computer, and it holds your saves and any content you create in-game. This is where you add mods, and store and custom content get installed here. If you move this folder out of Documents, the game won't be able to find it and will create a new folder when the launcher opens. Your mods won't be in the new folder and won't show up in-game, and neither will any of your saves.
It's probably best to just redirect Documents in its entirety to D, and then your saves won't be clogging up C. Here's a guide:
https://www.dummies.com/computers/operating-systems/windows-10/how-to-change-the-location-of-user-folders-in-windows-10/
The "dummies" part is a bit condescending (sorry), but this is the best guide I've seen so far, and it has screenshots to help.
If Origin is really installing files to C, clearing its cache and/or uninstalling and reinstalling it may help. But if it's only the game folder landing there, moving Documents will take care of that. The other possibility is that the game's installer is landing in C before the program files are actually installed to D. This isn't a problem. You'll know it's fine when the install is complete and there's nothing left on C.
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
https://help.ea.com/en-us/help/origin/origin/manually-uninstalling-origin/
