the original XKE Jag used 3 wiper arms, so did the US version of the MG roadsters (like th e78 midget), the morgan Aero 8 had 3 wipers, but i can't think of another old car which has 3 wipers so it must be something modern... like the FJ cruiser but it's 4.0L VVT-i engine has one exhaust tip.
are you talking about a concept car?