The parking switch inside of the wiper motor is defective. Replace the wiper motor.
How to replace wiper motor on a 1998 montero sport mitsubishi
No
You will have to remove the wiper arms, then remove the cowl, and then the wiper motor.
http://www.ehow.com/video_4936070_install-windshield-wiper-motor.html?pid=1&cp=1 (this is a complete video on how to remove and replace a wiper motor...very informative.)
Remove the wiring harness from the wiper motor. Remove the windshield wiper arm from the wiper motor. Remove the wiper motor retaining screws. Reverse the process to install the new wiper motor.
How do I replace the windshield wiper switch?
To replace a windshield wiper motor for a 1998 F150, first remove the bottom trim on the window. Then remove both wiper blade assemblies and all screws on the metal cowling. Remove the retaining clip from the wiper motor linkage and pull the controls rods off.
Very Carefully
Remove the windshield wiper arm from the windshield wiper motor. Remove the wiring harness. Remove the retaining nut. Reverse the process to install the new windshield wiper motor.
replace that black box on the wiper motor or sometimes you have to replace the motor itself
my windshield motor is working great, but the spline that the wiper arm sits on is worn out. do i need to replace the the motor or can i purchase another spline. thank you Ron