If you read this after a newer version than 1.0.5 of the mod is out, try it in the game itself first, as it might have been added already.

When the mod first came out on steam, i was really hyped about it, but when i was about to change all the settings how i wanted them, i saw, that you can not use mouse buttons like mouse-4, 5 etc. ,while the beta version allowed the use of them.
While some discussions showed that it was a known issue i was glad this problem isn´t unknown, but one discussion had a comment that solved this, you may have read it before, but this way more people can see it i guess.

(the comment was written by Epsilon Hardunkichud here: https://steamhost.cn/steamcommunity_com/app/619910/discussions/0/1470840994965488049/ )

>>>>>WARNING: Take a backup of the keymap.txt file to prevent possible problems connected to this file, so copy it somewhere else before you start, close the game while editing the file, i take no response for damaged games<<<<<

So what you want to do is to open your file-manager and navigate to documents/Square Enix/Just Cause 3/saves . Here you can find some folders that have a lot of numbers as names. If you installed the mod after the main game, the newest folder should be the one we want (not the folder called 0), for me the folder is called "4533017320", and open keymap.txt .

>>>If you are not sure, open the game, navigate to "settings > controls > car" and change the control to "look back" from HOLD R to f8 (or any other button), press "save changes". Now close the game and check every folder before you change any settings, by opening them, followed by keymap.txt . Check the 9th. entry in the document that says "action": "LOOK_BACK_CAM", under it it should now say "key": "PC_F8" (or the button you mapped it to), if this is not the case, check the other folders until it says that, if it says that, proceed as followed. (you can change "look back", back to HOLD R later). <<<

Here are all the controls listed in one document. You can quickly find out how it works by reading the names of the controls. For example:

"action: "PLANE_INC_TRUST", this is obviosly the control to increase the thrust while flying a plane
"key": "PC_MOUSE4" the control bound to it is for me mouse4

While this is for the mouse+keyboard controls, right after it, you can see the controller settings, they look like this:

"action": "PLANE_INC_TRUST",
"key": "PC_GAMEPAD_RTRIGGER"

But leave them alone as we only need the ones for the mouse+keyboard controls (You can clearly see the difference by checking if it says PC_(BOUND CONTROL) or PC_GAMEPAD_(BOUND CONTROL).

So, the only thing left to do is to scroll through this list and change the controls to mouse4,5 etc as you like by replacing the button after PC_ to MOUSE4 , MOUSE5 , etc. Only change the text after PC_ and leave everything else as it is. After that, just save the changes.

>>>If anything goes wrong, copy your backup-file to where you copied it from and over write the file (keymap.txt) by that. Now try again.<<<

>>>After you bound controls to mouse4,5,etc and you go to the game´s settings, the area that shows the key-name bound to an action you put to mouse4,5,etc, is empty, don´t worry about that, i did it and it works fine, if you see the "tutorial" at the right side of your screen everytime you restart your game like i do, the mouse buttons 4,5,etc are shown correctly. You will still not be able to bind controls to mouse4,5,etc from the game itself, you will have to do it from the document mentioned before<<<

There are also some debug controls that we can´t use, so leave them alone too.

>>>>>Screenshots<<<<<
>>>blank setting-entry<<<
https://cdn.discordapp.com/attachments/351093995440701462/351473938532007948/20170827231027_1.jpg

>>>correct-tutorial-displaying<<<
https://cdn.discordapp.com/attachments/351093995440701462/351475275998953483/20170827231623_1.jpg

I hope this helps you to get more out of your controls until it´s officially added.