transit t280 starting problem

[starbo]

hello im having problem starting my van. ive just tested the battery and it was reading 12.7 and i went to start it up and all the lights come on but it just wont turn over and theres a clicking noise. the alternator and startor motor are fine because they have been tested as well as the battery. any ideas? thanks

[winterheating]

chech the main earths and clean them, also main wire from jump point to starter clean allthem connections.