This video, taken at Bournemouth station in the 1980's, shows, amongst other things, how the 4TC units were operated. Towards the end of the video, a train arrives from Waterloo, consisting of a 4REP unit pulling two 4TC units (which are unpowered). The 4REP unit is uncoupled from the two 4TC units in the platform, and pulls forward into a carriage siding. The waiting Class 33 locomotive then pulls into the platform, and is coupled to the 4TC units. It then pulls the train on towards Weymouth, on the non-electrified section of the route.
On the return journey, the Class 33 pushes the 4TC units (controlled from the leading cab of the leading 4TC unit). On arrival at Bournemouth, the Class 33 locomotive in uncoupled from the train and replaced by the 4Rep unit, which will then push the train to London Waterloo.