My windshield wiper won`t work,i changed motor twice(windshield wiper motor),it still does not work?

i changed the winshield wiper switch.still it does not work.power is going to the windshield wiper motor-at all wires.my car is a 93 mercury sable;could it be the post module that goes to the wiper motor?why won`t my wipers work?|||Sounds like your Wiper Relay is burnt out. I had this same issue once before.|||Try your fuses!|||Actuator switch on the steering column can be bad or if you have delay wipe the timing relay could be bad.|||Sounds like a loose grounding wire (You measured voltage at the motor?).|||if you have 12 volts at the plug for the motor add a ground wire from one of the mounting bolts to a good ground should fix|||check ground wires