I recently bought a 1991 400 LS and was concerned that the trac warning light would periodically come on, "reset" after I turned the engine off but then somewhat later and without any sort of recognizable stimulus come back on again.
I finally concluded that the light might come on if the system was upset by a strong (outside) electronic signal such as from a police radar, an aircraft radar(overhead naturally), nearby cell tower's signal outputs, etc.
So I went to the hardware store, bought a small hunk of (copper) screen wire, cut it to size and positioned it over the Trac electronic unit at the back of the engine compartment. I tucked it around the edge of the unit as best I could and then used a bungie cord to hold the whole mess in place and thus creating a limited Faraday Change over the unit.
Although this is not a 100% solution it has greatly reduced the number of times that light comes on thus assuring me that there is nothing wrong with the trac system itself and hence no need to go running into a dealership.
If it continues to bug me, I think I'll try the black-electrical-tape-over-the-light-on-the-dash solution I read about earlier.
