For everyone who has Logitech G27 and would like to have the RPM LEDs working on their G27, simply download and install FanaLEDs from here http://www.fanaleds.com/
Once installed, Go to Help - Setup games automatically
Click Yes and locate your ATS or ETS2 main folder.
Now click Yes if your finished, or click No to add the plugin for another game.
Once that is done, you can now start ETS2/ATS and there will be a warning/confirmation window stating you have installed it, just simply klik OK and thats it, You can now enjoy your RPM LEDs on G27.
You are able to tweak a lot with FanaLEDs, change the RPM peak of colors, force feedback, etc.
To change the LED values for RPM go to FanaLEDs, Advanced - Car Settings. and change the values of the RPM first to RPM last, accordingly to your truck. NOTE: every truck will have different values for LED RPM.
For those who are too lazy to enter the above details
Open FanaLEDs
File -> Open settings folder
ets2.xml -> add following lines
<cars> <car type="default" first="0" second="0" third="0" max="0" shift="0" final="0" threshold="0" angle="0" /> <car type="FH" first="500" second="1500" third="2300" max="2500" shift="0" final="12" threshold="0" angle="0" /> <car type="FH16____Classic" first="500" second="1600" third="2400" max="2500" shift="0" final="12" threshold="0" angle="0" /> <car type="New____Actros" first="500" second="1500" third="2200" max="2400" shift="0" final="12" threshold="0" angle="0" /> <car type="Streamline" first="500" second="1500" third="2350" max="2650" shift="0" final="12" threshold="0" angle="0" /> <car type="TGX" first="500" second="1500" third="2400" max="2600" shift="0" final="12" threshold="0" angle="0" /></cars>
FanaLEDs will also work with other game controllers, like thrustmaster. however i only have G27 so i only know how to set it up with that.
Hope this helps anyone who wants RPM LEDs working in ETS2 or ATS.
I would like to give thanks to SteveTheCruel and Mudatrucker for expanding the configuration to multiple trucks in ETS2