Schlegel diagrams are used in graph theory to represent the 3-dimensional structure of a polyhedron.

Coxeter diagrams are used to represent finite reflection groups.

Argand diagrams are used to represent complex numbers graphically.

Hasse diagrams are used to represent partial order relations.

Alignment diagrams are used to visualize the alignment of different components.

Class diagrams are used to visualize the structure of a system.

Euler diagrams are used to visually represent relationships between sets.

Logic diagrams are used to represent the flow of logic in a system.

Phase diagrams are used to represent the different phases of a substance at various conditions.

I found some useful wiring diagrams online.