[B10alia]

If it's like our '05 Caravan, there's one pump and reservoir for the whole vehicle. I would suspect two pumps if the vehicle has two reservoirs, like our '95 had. If you don't have a rear pump and reservoir, look for electrical problems in the system.

 

[ImperialCrown]

There may be a single pump that is run forwards or backwards depending on front or rear spray selected. The direction of flow is controlled by fluid check valves. If the front sprays, it is either the switch or a blocked check valve.
The pump is mounted at the bottom of the washer fluid reservoir. Have a pan ready to catch the fluid if the pump has to come out.