Grea,
there were few areas in Birmingham that were served by trolleybuses. The first route, numbered 7, was to Nechells. This commenced in 1922 which replaced trams also route 7 and ran until September 1940. It was curtailed due to fears that overhead sparking with the electrical overhead wiring might give the Luftwaffe clues particularly as there was very heavy industries in that area at the time. It was intended to recommence after the war was over but it did not happen. Bus route 43 replaced the trolleybuses which were put into store for the wartime period and scrapped shortly after.
The other part of the city served by trolleybuses was places along the Coventry Road. Trolleybuses replaced trams there at the beginning of 1934. The new Rover factory in Solihull was naturally Midland Red territory but the were unable to deal with the large amount of workers employed at Rover. During the war (WW2) BCT were given permission to construct a trolleybus route extension to Rover. Midland Red took over again in 1951 after the trolleybuses were replaced by diesel buses.
Some reasons that trolleybuses did not survive longer was due to great strides made with diesel buses and the fact that around 1950 there were approximately 1500 diesel buses and just 75 trolleys and as such were not considered needed.
Trolley were, at one time, considered as tram replacements. The Dudley Road and Hockley direction routes were considered in 1939 but it was not implemented much to the dismay of West Bromwich Corporation, who were in favour of trolley buses and who shared some of the routes that ran via Hockley. The attitude by West Brom was understandable as nearby Walsall and Wolverhampton Corporations both operated trolley buses.