Faith is at Muffington Island in the plane with the sign that says "Queen". You first have to deal with Wendi.
This is the low-spoiler guide for "Convincing Faith" puzzle in Leisure Suit Larry - Wet Dreams Dry Twice. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.