the electric power steering does take some other information from around the car, like vehicle speed but as its all contained inside the car with only the motor on the steering rack
but to be honest I'd be very surprised if the engine bay wiring loom issues have effected the power steering
but you are right in saying that these cars can have issues with the power steering 'module'
you said the charge for replacing the loom was £1000, did you manage to negotiate this down? if so then good job as the job to replace it is actually quite involved and takes about 3 hours labour (at a typical hourly rate of £75/hour) and then the parts are about £300