78 DeVille small electronic box near rear exhaust w/lever on it

My 78 Deville has a small black, flat, box with wires connected to it and a metal rotating lever on it. It's located under the car near the rear on the
right side. I believe it connected to the factory exhaust system in some way but my exhaust system has long since been replaced with a custom performance system that now exits just behind the front wheels. My question is what is this box for and should I remove it or position its' lever up or down? I've also noticed that my small (little dot on dash panel) orange emissions light is lit continuously. Is this why?
Thanks for any help!!!
Freddy www.goldiesplating.com
Goldies Plating Service "New York's Finest Premium Gold Plating Service" online at http://www.goldiesplating.com
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Never mind.... My Bad. I've been told that this is for the ALC (automatic level control) HOW embarrassing!!!!
Freddy
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