car in trust - how do I sell

Hi.  The answer to your question depends on whether the property was titled in the name of  the Trust or simply owned by your mother (and thus in her probate estate).  If it is in the estate, you will need to open the estate (by filing a Petition) to get something called "Letters of Administration."  The Letters will allow you to sell/transfer property in the estate.  

Otherwise, if say a living Trust owns the property, the Trustee would simply sign over title to the property in that capacity (consistent with the trust terms, of course.   I hope this helps point you in the right direction.  Of course, this post does not substitute for legal advice and the specifics of your case and  the language of the will / trust may impact what you can do.