A grand marquis wiring diagram can be found in a Chiltons or Haynes auto repair manual.
The stereo wiring diagram for a 1988 Mercury Grand Marquis is available from a factory service repair manual. These manuals can be found online and PDF. format.
autozone.com
at the junk yard
need wiring diagram for radiator fan control
Yes, there is a free stereo wiring diagram for this car. It is in its maintenance manual, or a person could ask for a print out at an auto part store.
owners manual.
When making changes to the fuel system, a diagram can help guide in the repairs. A fuel system diagram for a 1993 Mercury Grand Marquis can be found in its maintenance manual.
Yes, a person can get a diagram of the PCV valve location in a 1989-1999 Mercury Grand Marquis. This diagram would be located in the maintenance books found in auto part stores.
Wiring Diagrams Ford Crown Victoria/Grand Marquis 1989-1998 from AutoZone DIY http://www.autozone.com/az/cds/en_us/0900823d/80/17/3d/a8/0900823d80173da8/repairInfoPages.htm
Try Autozone.com - they very likely have an on-line illustrated repair guide for the '93 Grand Marquis.
Look in the owners manual.