I installed the TS4 program to my largest drive. D drive but the EA folder (and therefore Mods folder) landed on my C drive (which is tiny and prone to hysterics)
I honestly can't remember if I chose to put the EA folder there, or if it was a default at installation.

I'm putting off downloading mods because the c drive is only really designed to squeeze windows in plus a little on top.
Can anyone make a suggestion?

I would make sure that your Sims4 folder is where you want it, but make sure your Mods folder is inside your Sims4 folder. You should try and see if moving your MyDocuments>ElectronicArts>TheSims4 folder to the D drive lets you run the game. Your Mods folder will always be inside that folder, as a subfolder, along with your TRAY folder. If it doesn't work when you move the folder, or regenerates a new one, you'll know you can't move it.

This might only work for .package mods. Update the resource.cfg file in your current mod folder to add PackedFile D:/<Your choice of folder here>/*/*.package then store your mods in there. I got this idea based on how you would create subfolders here: http://modthesims.info/showthread.php?t=531644

Reinstall the game in your D drive and see what happens ... I'm not sure it will work, so backup all your game files and try at your own risk.

You don't need to re-install. The result will be the same. Software and especially games deal with user specific data like game saves and configuration (and mods) by putting them in your My Documents or Users folder on windows. This way, if another user logs on and plays the game under their account they won't touch your saves or configuration. Sometimes, applications have options to let you save these settings somewhere else other than the users folder, but I haven't explored the sims configuration options that much to help you with that sorry.

Thank you for all the ideas.

@TamiraA when I saw your post I planned to try the technique you suggested, as I know I want to make subfolders anyway...then I got an interesting answer over at EA Help HQ that I could try using mklink which fools the pc into thinking a folder is in a different location,
http://www.sevenforums.com/tutorial...ks-windows.html
With a bit of hand holding I managed to locate both my screenshots folder, and mods folder over to my larger drive, but the program still think they are on my C drive.

So this means I can separate out the task of making subfolders for another day, which means less work for my overloaded brain!

Thank you for sharing your solution I have never heard of MKLINK until today, so I'm very happy with learning something new

As an update to this, in a flash of inspiration (insert blue simmy halo ) I moved my saves folder to a synched dropbox folder and this seems to work fine.
I think I could probably have managed this auto-backup via tweaking my dropbox settings, but at least I feel organised this way