The diagrams for the 82 & 83 US version cars list fuse #4 as powering the;
turn signals
interior lights
stop lights
radio fuse
clock
door buzzer
mirrors
In 84, the fusebox light was added to the same fuse.
Sorry, no 85 or 86 diagrams.
None of these devices are powered through the ignition switch (fuse #4 is unswitched hot) so I'd rule out the ignition switch.