I want to clear codes on our 99 300M they say to disconnect battery terminal. Battery located under air filter. Can we just disconnect negative terminal line?

 

yes U can just undo the neg cable up top a little FYI if I were u I would get the code number first b4 erasing them second unless U fixed what the issue is more then likely it will come back 3rd if U really fixed the issue the light will go off on its own after a few days the computer will see what ever it was corrected and turn it off.