Where is the fuel relay located on a 1991 Plymouth sundance?

The Fuel pump is inside the gas tank and only a qualified professional should attempt replacing it.

First the fuel tank needs to be emptied completely. Then the tank needs to be dropped. Then using a brass bar and a brass hammer, so as NOT to cause sparks there is a round plug with the fuel line coming into the tank, using the bar and hammer tap the plug open there you will find the fuel pump. The fuel filter is outside of the tank follow the line from the tanks and replace the filter also.

GOOD LUCK! This is VERY dangerous because there need to be good ventilation and the car should be lifted off the ground by at least a foot with chocks.