Shunt signals, whether mechanical or position lights, are the authority to proceed on a specific route(s) as far as the route is clear or until the next stop signal. Old FR Point Indicators were just indicators of the position of the points - they gave no authority to proceed.
'Running shunts' are/were on the main line and were in the direction of the main route. They were first cleared before the main signal, to their rear, was cleared. The shunt signals at Harbour, pre 2014 re-signalling were running shunts.
Since the FR revival new shunt signals have been installed at various points and periods. These have usually been ex BR disc equipment mounted at a low level. A double one was sited at the crossover at the throat of the old Harbour Station layout from Spring 1967 and there was later another one at Dduallt bottom points when first signalled in 1972/73. A high level one is mounted on a signal post with an illuminating light as part of the 2014 Harbour Station resignalling. Position Light shunt and subsidiary signals (ex-BR) have also been used in modern re-signalling schemes.
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