Employer Tax ID for 401(k)

[Guest bouncingsoul]

I understand that some sole proprietors who use their SS# as their Employer Tax ID would need to set up an EIN to establish a plan. Is this correct? Does anyone know where I can find this language?

[WDIK]

Form 5500 instructions for line 2b.

[Guest Pensions in Paradise]

Also in IRS Publication 1635.