2010 Powershift Accelerator Pedal and Brake Switch errors

Hi All, 

I have recently purchased a 2010 S Max 2.0TDCI Titanium Powershift with 90k miles. 

A week after purchase the gearbox failed on me and I made the decision to have it rebuilt rather than cut my losses. This cost just over £3000 but interestingly during the adaption process they were struggling with throttle pedal fault codes preventing the adaptions being completed. In the end they fitted a second hand throttle pedal and all was good. 

Since then I have completed over 1500 miles without any issues until recently the car went into "Engine Malfunction mode" where no matter what you do it wouldn't rev at all and the engine would idle at about 1200rpm. The AA were called out as I was on holiday and their diagnostics equipment indicated a faulty throttle pedal. After it was recovered home (200 miles at a cost of £480 might I add!) I plugged the car in using FORScan and got the following codes:

P0120 - Throttle Pedal Circuit A

P0504 - Brake Switch A & B Correlation

I then replaced the throttle pedal and both brake switches with new OEM items and cleared the fault codes. The car managed to last 20 mins before the same thing happened and the codes appeared again. 

I have started tracing the wiring from the accelerator pedal back under the carpet towards the centre console but haven't found anything obvious yet.

My question is are there any known wiring issues in this area or ECU faults? or even other issues that cause these symptoms? 

Thanks in advance for your input