Where is the air suspension module located on a 1999 town car?

On a 1999 Lincoln Town Car, the air suspension modules (air springs or air struts) are located at each corner of the vehicle. There's one on each front and each rear wheel. They're not easily visible without some disassembly; they're integrated into the suspension system itself. You'll need to look underneath the car to find them. They're typically cylindrical and somewhat large compared to other suspension components.