Wow. I have the very opposite issue - I would be terrified to run into my T or see her in any other context, even seeing her name in the telephone book would freak me the hell out!
I really don't know what to advise, because I can see both sides of it. Maybe it's projection when I think it would be better to NOT know (i.e. don't tell your T - I can only imagine if I was told that by another person I'd be terrified and feel terribly violated). But then, like others have said - it's about honesty and about change and your T is probably trained to deal with it.
Will you be honest with him if you tell him and he asks HOW you came to know where he lives? This might help in avoid it happening with another client. I know many Ts have PO box addresses, and go to great lengths to protect their privacy and that of their family's, often not going in the telephone book etc.
Far out, I really am having a pretty big reaction to the concept of this situation .. it says more about me than you OP of course. I think I'm just feeling horrified at ht mere thought of my doing anything like that, let alone contemplating TELLING my T - that is pretty brave of you.
Maybe you could 'test' the waters - say you are on an online forum or you read something online about how sometimes clients have stalked their Ts, and you wondered if that had ever happened to him, and is it something he would worry about? The drawback of this though, would be if he reacts very negatively and you won't feel you can say you have done it to him.
Although, driving past his house is waaaaaaaay different to standing outside his house in the dark and peering in the windows …
I had a friend who when at the heights of her BPD, she sent her psychiatrist razor blades in the mail - to his private home address - with her blood all over the paper inside … she also phoned his electric company and got his power disconnected … yet she was honest with him and he still saw her.