Mr. Dawg, my first time to post, so excuse if doing improper. I have a 97 Grand Marquis, so doubt if fuse chart might be same as different engine, etc than 91. Looked through two 'auto parts' manuals purchased and no help.
I would check the brake switch first, mounted on the upper area of brake pedal. May need to drop kick panel to get to. Remove the electrical plub from switch and check circuits with volt meter. If don't have one, place pig tail wire into both terminals (naturally, remove little of the insulation, first) and see if brakes lights are on with wire in place. If so, that's it! Be careful and do not ground the wire to the surrounding metal, as the brakes switch feed wire is always hot.
Since tail light and prob license lights burn, tend to think the ground wire is o k. Turn on your flasher switch and check to see if front and read lamps flashing. I think the flasher circuit by-passes the brake switch. Again, points to the Brake switch.
And tend to think the turn signals working front and rear, since no mention of they not working.
Some of these electrical problems are tough, and makes you realize a good technician is worth his money after learning his trade. And no, I ain't in the auto tech field, just a shade tree mech. and worked in son's auto garage couple years after I retired.
Check your local library and may find Chilton manuals, including wiring manuals, on shelf. Good Luck!