The following are diagrams courtesy of Tmoss & Stang&2birds
Fuse box layout
Ignition switch wiring
The only 20 amp breaker I see is the one for the power windows, and it only has power when the ignition switch is in the Run position.
If you are looking at something else, use the diagram to reference what it is.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.[/b]