The heater motor has twelve volts to it at all times. The switch grounds the motor to turn it on, plus the switch sends the ground through different resistor coils to vary the ground’s resistance and blower speed. Typically, the old hot wire is damaged where it enters the motor end housing.  If that is the case, you will get an intermittent short from the hot wire to the motor case. If it goes to a full short, it should blow the fuse.
It is possible to disassemble the motor housing to reattach some new wires, but might be easier to replace the motor, since it will come with new wires.

Of course, it is always possible that something else is causing the short, but the issue I described is the easiest place to start troubleshooting.

Huskinhano wrote:

Another possibility is the motor wasn’t grounded. When you touched the motor and something else you completed the circuit and got the shock. Make sure the motor is grounded if this is the case and everything will be fine, no more shocks.

I’m a electrician by trade. The white wire is called the “grounded conductor” and it means exactly that. The white wire is connected to the ground. Now we all know you can touch the white wire and metal and not get a shock. That’s true most of the time. How ever if you disconnect a white wire from the circuit, that wire is no longer grounded and if a switch is on and you touch that white wire and ground, you have 120 volts going to you because you’re part of the circuit now

Hi , well the worst thing is that i have 12 v on case also if i disconnect the wiper from circuit ! 
 

If I remember correctly the wiper motor is mounted on rubber grommets so the case may not be directly connect to ground. That is why it may be able to have 12 volt positive to it without blowing a fuse.