British Rail Drivers Manual - Fault Finding Data and Charts for Class 56 Locomotives  
Date of Issue: Unknown - Issue 2  -  BR 33056/44.

More information can be found here Wikipedia - British Rail Class 46  -  Derby Sulzers Website 
More Information Regarding Preserved Class 46 Locomotives can be found on the following websites:  Preserved-Diesels  -  Llangollen-Diesels