THe LED light should already be there. You just need to find the diagnostic module, near the battery, and take off the black plastic cover. Turn the ignition key to "on" position (without starting, but with all instrument lights on), push down the button on the diagnostic module for about 4 seconds and then count the number of flashes of the LED light right next to the button. One flash means no codes - anything else has a meaning. Then do it again to see if you get the same number of flashes or a different number. Keep doing until it repeats itself. Then you hold it down for 8 to 10 seconds to clear the codes - one at a time. Again, there's lot of stuff in the archives on this, including a list of all the codes. This assumes you have the LED light and button - I believe 95 was the last year.