Docks station was renamed Birkenhead North. The site on which the Merseyrail Electrics depot now stands was the the Wirral Railway's loco shed , works & carriage sidings. The tracks passing the depot were goods lines to the docks & a connection to the Birkenhead - Chester line at Grange Lane .
Not quite Birkenhead North on the current site was not built until electrification - it was a carriage shed (for loco-hauled coaches) before that.
An even older carriage shed was built on the other side of the line.
Up until electrification North shed was bang in the middle of the afrementioned goods line.
Please see the attached link for further details:www.disused-stations.org.uk/features/bidston/index.shtml
Please see the 1899 map on this link on which there are 2 Engine Sheds mentioned - the most westerly in the main line Great Central Bidston shed - the one where North Traction Depot is now - is incorrectly tagged (see text) and the actual shed was the most westerly building in the group that forms the area labelled good station - the goods station was on this site too using the other buildings.