What is this??

I just gained ownership of a 1994 Park Ave and was rotating the tires this morning and found a gadget that I'm not familiar with. On the right rear control arm is a rod about 8 inches long attached to a black box about 5" square on the body. I know it is measuring body/suspension movement but what is it for?? I dont have air springs I know that much. I'll try to get a picture of it later. Thanks for the help.

You don't have air springs but check your shocks for a rubber bag around them. They are air shocks.

Hmmm I never thought of that, only gave them a cursory glance. I'll have it on the lift tomorrow at work and I'll take a closer look and snap a pic or two. Thanks for the help.