Once you have the major minor and diminished triads mapped out on the fingerboard, it's time to add the 7th interval.
There are two 7th chords built from the major triad, Maj7 and Dom7. The difference between the two is whether you add a natural 7th to the chord or you add a b7:
The easiest way to see the 7th interval is to work backwards from the root. Remember that the root and the 8th are the same note. Therefore, it is easier to work backwards from 8 than it is to work forward from root.
Now, when it comes to adding the 7th to the minor and diminished triads, you only need to be concerned with the b7 at this point. The major 7 interval (min/Maj7 chord) and the bb7 interval (o7 chord) are not native to any of the minor chords built from the major scale or the modes of the major scale. These chords are covered in conjunction with the harmonic and melodic minor scales. (be sure to review the intervals lesson and the 7th chord lesson if you are not clear on 7th chords.)
Here are the minor and diminished triads with the b7 added:
Now that you have the triad and 7th chord plotted over the entire fingerboard. It's time to turn our attention to scales and modes. Most people tend to think of chords as static and scales as fluid. In other words, chords are something you hang out on, while scales are what you use to move around over the top of the chord. While this view is true to a certain extent, it's important not to ignore the connection between the chord and the scale.
Chords can function on two levels. First and foremost, the chord defines the "harmonic climate". That is to say that the chord dictates whether the sound is major, minor, or dominant. Secondly, the chord defines the "target tones" of the scale. Every scale is composed of notes that create tension against the harmonic climate and notes that are at rest with the harmonic climate. The notes that are at rest with the harmonic climate are the "target tones" - the notes that your melodic phrase should lead toward or come to rest on. The target tones and the chord tones are one and the same.
This brings us to the arpeggio. An arpeggio is nothing more than the chord tones used in scale-like fashion. Arpeggios can be used very effectively in melodic playing due to the fact that they are composed entirely of the target tones of the scale.
I would suggest that you spend some time learning to create melodic lines and phrases using triad and 7th chord arpeggios only. This will teach you a great deal about how to use scales more effectively.