I BELIEVE that ( fuse #21 ) is a 15 amp fuse for the hazard flashers on your 1998 Ford Explorer Sport ( at least it is on the 1998 Ford Explorer four door )
because there are two diffrent flashers 1 for the flashers and 1 for turn
I believe the flashers are on a separate fuse than the blinkers, that is where I would first start to look, is the fuse box
No gurarantees, but most car signal flashers are plugged in at, or near the fuse box - try there.
Its the 1x3/4 inch silver round fuse in the fuse box
If the flashers remain on after you have pulled the fuse, you may have pulled the wrong fuse or it has somehow been bypassed.
There are two different flashers on vehicles. 1 for the turn signals, 1 for the hazard flashers.
( Fuse # 25 ) - 20 amp - cigar lighter , power point , emergency flashers
rear tail light fuse
Click on the link below Click on Owner Guides The owners manual ( which includes the fuse diagrams ) can be viewed online
There is a large round chrome fuse called "The Flasher Unit". It is located next to or close by the fuse box down by the drivers feet, or there might be a fuse in the fuse box,the fuse box is labeled.
You might just need a new flasher or a fuse.