I have a question about a 1997 Seville STS

Before you take it to a shop for a (likely) expensive diagnosis and repair, check the ground(s) at or near all the light clusters. Most likely you have a missing/loose/corroded ground wire, probably in the rear. Usually easily accessed from the trunk. Good luck!

expensive diagnosis and repair,

9 times out of 10 you will find a burned out light, turn on your signal light and take a walk around the car to see what isn't working. Or look for a burned socket, this is what holds the bulb in place. Good Luck

Electrical problems can be the hardest thing to find. I've had a couple of electrical problems that weren't "normal" like a bad ground, etc. Once on a mid '80's GM product I kept blowing fuses on the turn signals a couple weeks after I bought the car. I checked both ends of the car for grounds, etc. but to no avail. So I began to remove the door sills on the left side of the car where the wires ran to the back. What I found was staples thru the plastic left rear door sill in a effort to hold the carpet in place. However, the staples went into the wiring as well causing a short across from one wire to the next, or a bad ground and blowing the fuses. I asked myself, why now? Why did it decide to show up after a couple of weeks? The only thing that I could summarize is that my little girls were stepping on the sill when entering the car and drove the staples down into the wiring. Of course this had been a bad fix at the dealership to begin with and the staples should not have been there in the first place. Another time in a mini van the rear gate wiper would come on and off by itself. Trying to find the fix for this one was driving me nuts. By chance I replaced the battery before winter set in. I like to have a good battery in the winter. And guess what? The problem no longer happened. Bad batteries can cause many strange electrical problems. Many times the repairs on a car are usually the simple things. So might I suggest checking the age of your battery. If it's over 3 yrs old have a mechanic give it a good testing, and not just for draw down. If it's much older than 3 yrs replace it with a good brand name battery like interstate and not some walmart or other dept store off brand. My two cents worth. f.b.