Hi,
To become a Lead Auditor for TS 16949.
You need to be employee of a certification body like BVQI, UL, TUV, DNV etc.
They will nominate you on behaf of them, then only u r eligible for the the qualification.
Qualification if done by IATF- mainly SMMT or AIAG.
Visit web site
www.iaob.org
To become a lead auditor for other product u can apply to any certification bodies who are conducting lead auditor courses.
hope this may help u.