A lot of times, he used just the plain old major scale with occasional alterations such as the b9, #9, b5, #5, and b7 (read: he used every note available). When to use these? Whenever they sound good! Use your ear when you solo. Play a jam track, like a one chord vamp and listen to how each note interacts with the chord.

Check out a book such as "The Best of Wes Montgomery" and you can study how he soloed.