Think of something akin to a small, industrial-looking electric pump, about the size of a large soup can or perhaps a bit longer and thinner. It likely has some mounting brackets for attaching it to the car's frame or undercarriage. You won't find anything flashy about its appearance.
To be absolutely sure you've found it, you should look for:
* Location: It's usually located in the engine bay, tucked away somewhere, or possibly under the car near the suspension components.
* Air lines: It will have at least one, and possibly two, air lines connected to it. These lines will lead to the air suspension components.
* Electrical connection: It will have an electrical connector for power.
Without a picture of the specific compressor for that model year, it's hard to give more detail, but this general description should give you a good idea of what to expect. A quick online search for "1992 Lincoln Town Car air suspension compressor" along with images might be helpful in visually confirming its appearance.