Answer:
First a caveat — Trusts and their control are typically matters covered by state laws. For definitive guidance on your question, you should consider having local bank counsel review the trust.
That said, it is usually the case that trusts are controlled by the trustee(s) identified in the trust document or, if those trustees are no longer in the picture, the successor trustee(s). One of the reasons for creating an irrevocable trust is to remove control from the grantor for certain legal, estate planning, and/or tax liability purposes, and allowing the grantor who is not a trustee to sign on the account would typically defeat such a purpose.