Power of attorney question

Whoever told you they need a power of attorney, has no idea what they are talking about.  Powers of Attorney in Texas (and everywhere else for that matter) are revoked upon death.  So even if your son had given you his power of attorney, it would no longer be a valid document.  What you don't say in your question is what you are trying to do with his vehicle.  I don't know where you are located, but most probate and estate planning lawyers will spend some time with you on the phone for nominal charges or for free to get you pointed in the right direction.