Best approach:
If your parent organization is already registered to QS or TS 16949 or 9K, then the lab manual only needs to address the additional extra requirements of ISO/IEC 17025.....don't reinvent the wheel.
However, some things to watch for, ESPECIALLY if you seek accreditation under 17025.....
Management review - regardless of any other topics or whether it is combined with the parent's review - MUST include the prescriptive requirements of Clause 4.14.1.....Internal audits MUST SPECIFICALLY address the internal lab, even if combined with the parent's internal audits.....any information published by the internal lab, even if only going to the parent MUST meet requirements of Clause 5.10 (sub-sections as applicable).....watch the calibration and traceability parts, your calibration provider including sub-contracted cal or testing must be able to support your accreditation, which means they must meet the same requirements, whether accredited or not.....and if not, then you take the 17025 checklist and a technical person with the background in what the vendor/sub is doing for you and perform what amounts to an accreditation assesment on them.....
This is not easy, however we have seen that labs that meet these requirements often have a higher level of performance and a lower level of issues.
Hope this helps.
Hershal