I am afraid I have only come accross this before on Coopers and not Cooper S's and am not sure if the S's suffered the same but on the normal cooper, where the harness goes into the throttle body were bad for breaking (until the modified harness came out in 03 I think!) if it is the same problem, any auto sparky should be able to check/repair the harness for you in under an hour, if you are confident, you could even look yourself, the last one I repaired was really obvious once the conduit was removed.
Hope this helps.
