The thing is, refilling yourself is not really a good idea.
The system has to be brought upto the correct pressure. It is very easy to over pressueize it with those cans.
If you still want to try it, yes it is the line behind the alternator. If you have a tower brace, remove it, and then hook up the can to the line BEFORE starting the car. It's just safer that way because, well you see where the line it in relation with the belt and alternator pulley...
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