Which is required (TIN or EIN) on a revocable living trust account where the trustee has resigned and the successor trustee is now in control? The successor trustee opened the account in the trust name and the trustee has never signed the signature card.

Are you sure this is living revocable trust and not a living irrevocable trust? (The grantor has given up control and the trust has been funded during the grantor's lifetime.)

From my experience, when the grantor is not the trustee the trust is usually opened up under an EIN. The original trustee should have been the one to open the account and should have signed. Since the horse is out of the barn, the successor trustee needs to sign the signature card just as the original trustee should have. If your bank uses one you would want to use a successor trustee affidavit signed by the successor trustee to cover your bank.

You should have the trust reviewed to confirm the type of trust. This will help in determining the correct set-up.

A TIN can either be a SSN, EIN or ITIN.

There are a number of features that can make a trust a "Grantor" trust where use of the grantor's SSN is acceptable. One is where the grantor serves as trustee. Another is where the grantor has a power of revocation, something he can have regardless of whether he is a trustee. Another is when the grantor retains the power to change beneficiaries. There are others.

As noted, your choices are between an SSN and an EIN, but there is no way to know the answer to the question without reading the trust.

In many cases, if a Trust has been a living revocable trust using the grantor's SSN and the grantor is the Trustee, it becomes irrevocable and must have an EIN when the grantor/trustee dies.