This guide was copied from my guide for Farm Expert 2016. Since both games are nearly identical the same method applies.

Navigate to your game's primary folder. This is found in:

(Or you can find the game in your Steam library, right click it, go to properties, browse local files.)

In that location you will see two music folders.

One of them says "music". It contains the game's original soundtrack. You can leave that one alone.

The other one is

That is the folder where you put your music. The developers were nice enough to include this for you.

Be aware that your music files must be in the .ogg file format in order to work in the game. There are many websites online that you can use to convert your files for free without having to download anything. Simply convert, put them into the my_music folder and you're done!

You'll know if it works when you get into a vehicle and hear your music playing. The songs play by the order they are placed in the folder. But anytime you exit a vehicle the currently playing song will end and as soon as you get back in the next one will begin. To get the original music back simply delete your music files from the my_music folder and the game will revert back to its original soundtrack.

(I have been playing the game while listening to popular country artists and the feeling it generates is worth it.)

That's all there is to it. I hope my guide will be useful in giving you a better in-game experience.

Thanks for reading.