Outer Limits 4x4 Board

Ive recently fitted a factory locker to my gq, Ive spent hrs mucking around with now but it only engages like 1 out of 5 times?
I havent got any soliniods im just coming from the engine to a vacuum resivior, 5way valve then. 2 hoses back to the diff,

should this work or has anyone done it before just off vacuum?

Starting to think its not supplying enough vacuum from the engine? As its running a decent camshaft,
i pulled off the booster hose on my vs caprice 5ltr and its got about double the suction,
thanks..
Jess

I've done exactly the same thing in mine - just running off engine vacuum (TB42). It won't always engage straight away. it won't click in until the dog teeth line up.