A booklet from the from the 33003 series, this also covered the 79xxx series vehicles. Earlier editions seem to cover those vehicles only.
The 33056 series drivers instructions, which replaced the 33003 series in the 1970s, specifically stated that they did not cover the Class 126 vehicles. No alternative has been found.
Summary
Description
Works Photos
Diagrams & Design Codes
Drivers Instructions
Numbering
Liveries
Operations
Images
Details about the preserved Class 126s can also be found here.