On an L D V minibus what is the Brown with yellow trace cable connected to?

On the L D V minibus, the starter motor is giving indications of a bad connection at irregular intervals. All cables connected to the ignition switch and starter motor are correct, solid good joints. There is a Brown with yellow trace cable that i am unable to trace. Is this connected to a safety or fuel circuit. Ialso have no circuit diagram.
Thanks in anticipation, Ian