How can we check different wires' continuity on a vehicle ? where we need to put the + ve & - ve probes ?

when you're checking for continuity, you are checking to see if a wire is intact or broken(ohms-resistance). I believe you've got your tests mixed up. You're checking to see if you have 12 volts at your windshield wiper motor. You put the red read on the power line coming into the motor and put the other lead on ground. If you've put the leads on the correct wires it will read what the battery reads. I sense you don't have an understanding about checking for voltage in a car. If this makes any sense to you and you need more help, write back and we'll chat/