We have gas turbine mark II.
When put AC lube oil On, DC lube oil Off.
Start ok but when returned DC lube oil to On Start DC and cutting AC.
63QA is ok.
Pressure is ok.

 

I would really need to see your Lube Oil P&ID and your DC Pump MCC wiring diagram. From memory, I think that you should have a 63QL which controls the Emergency Pump, 63QA usually controls the Auxiliary pump. I am guessing that you have a problem with 63QL and also that you have an electrical interlock between 88QE and 88QA, this would all fit the symptoms.

Please reply when you have checked.