If the exisisting cable is still inplace just trace it when you fit the new one. As for the water damage it is not unknown for the heater matrix to leak, i would think this is more likely than 'drainage holes'
hi thanks for that but my husband is changing the engine and the clutch cable had come away, apparently its come away from the pedal and he can't see how to fit it back. who'd have a teenage son!!!!!!!! past his test on the thursday blew the big ends on the friday lol