Horn stopped working
Should have two horns, a high and low. Since you don't have a horn at all I'd guess the fuses. Otherwise you get a multimeter, disconnect the two leads to each horn, put a probe on each and have someone whack the horn. If you get 12 volts, the horns are bad.... but I doubt both high and low would both break at the same time
If you have keyless entry try the panic button on key fob and if the horns work its not the horns or the the relay (now if they don't honk its either the horns (there are two of them) or the relay) if not its in the steering wheel horn pad or contacts under the horn pad. In which you have to remove the horn pad to get to the contacts. (NOW REMEMBER THE HORN PAD ALSO CONTAINS THE AIR BAG. You to disconnect the battery or AIRBAG fuse for at least 15 to 20 minutes before removing AIRBAG. Every AIRBAG is a little different on how to remove it (they are usually held on with clips on the under side of AIRBAG that have to be released. I would check online on how to remove AIRBAG thats how I found how to remove mine once you find out the trick they very easy to get out.
Looking for a Used Grand Marquis in your area?
CarGurus has 1,706 nationwide Grand Marquis listings starting at $1,000.
Search Mercury Grand Marquis Questions
Mercury Grand Marquis Experts