If the service engine light is on, this is in a way a good thing. This means that your vehicles computer has detected a problem and the computer has stored this information for you. Now the trick is how to get that information from an older system like you have (they changed the system in late 1996). You need to find the data link connector which should be under the dash on the drivers side of the vehicle and I believe yours (don't quote me on this) is on the right side of the steering column by the brake pedal or even mounted on the bottom of the dash (same area though). Below is a picture of what this data link plug looks like. Now have a peice of paper and a pen also a paper clip (one of the bigger ones are better. Now take that paper clip and kind of bend it into a "U" and insert one end into the letter "A" spot on the plug and the other end in the "B" spot on the data link plug. After you "jump" A and B turn your ignition switch to the on position without starting the vehicle and look at your check engine light.. Here is where the pen and paper come in. The check engine light should start blinking. The begining or starting blinks should goes as "blink" (one blink) - Pause - and the "blink blink" (2 blinks). This is a code 12. A code 12 means the system is working. It will blink a code 12 three times. After the code 12 there will be a litttle longer pause and then another code(s) should start. this is where the counting comes in. so after the code 12 and the pause, if it blinks 4 times - pause and then 2 times, this is a code 42 ( am using a code 42 just as an example). It will blink the code 42 (or whatever code) 3 times and then move on to the next code. There may only be one code but if there is more they will go in order. When it goes back to a code 12, the diagnostic is complete. Write down what codes you retrieved and these codes will lead you to the direction of the problem and there are testing procedures that go with each code. Until I get those codes, I am unable to help you any further. Once you get code(s) you can reply/comment here what they are or feel free to email me directly at email@example.com
with your vehicle information (make, model, year and engine size) and I will be happy to try and help you diagnose what the problem is such as a sensor or whatever along with tesing procedures so you're not just replacing parts that are not needed. I know this was a long explanation but it's the only thing to be done at this point. Hope I was able to explain it to you so you understand and I was able to help.