There are many different types of motors and many different processes to make them. Personally I have no experience with making electric motors, but I am sure that while there are surely some processes in common, process equipment will differ. You would have to tell us a lot about the process equipment and the motor its self, as well as the process flow.
Hopefully someone will be able to help, but at this time there isn't much information to start with.
The method to start should be the same for all process FMEAs. It doesn't matter if it's a DC Motor, a molded plastic bottle, or an aircraft engine.
Start with the process flow. Break down each step in the flow as detailed as you can and identify what could go wrong (failure mode) at each step. For each failure mode, identify what is the effect and give it a severity ranking (1 to 10 or whatever scale you're using).
For each failure mode identify the cause(s) and give it a ranking (1 to 10) for how often it is expected to occur with the current process.
Now for each failure mode list the controls you have in place that will detect the failure. Give the controls a ranking (1 to 10) for how likely it is to detect the failure.
The Risk Priority Number is calculated by multiplying the severity ranking by the occurrence ranking by the detection ranking.
After you've evaluated the whole process you should identify where the highest risks are and determine actions to take to reduce these risks.
If you don't already have an FMEA manual I would suggest that you get a copy of the AIAG FMEA manual. It has good guidance and tables to use for the rankings.