M30 (E34 BMW 535) injector wiring

[(steven)]

I am currently rebuilding the top end of an M30 engine out of a BMW 535. I am currently trying to get the inlet manifold off however to do that I need to disconnect the injector wiring. Any ideas how I do this? There is a plastic case on top of the manifold which feeds the electrics into the injectors. I've opened it up and undone the allen bolts but the connectors won't budge. Any insight on this would be appreciated.