To find it, you'll need to consult your owner's manual. This manual will have a diagram of the fuse box(es) and relay locations, showing what each one controls. Look for diagrams showing the fuel pump, fuel injection, or engine control system.
If you don't have the owner's manual, you can often find a digital version online through a site like a Chrysler parts site, or a dedicated automotive repair manual website (like Chilton or Haynes). Searching for "1990 Plymouth Acclaim fuse box diagram" will help.
Important Note: Working with the fuel system involves potential fire hazards. If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic.