Right I've just got an SDi for my son. The brake lights stopped working so I took the brake light switch out. It looked easy to take apart as it was the old style type. Once apart I found one of the contacts looked a little burned so cleaned it all up, re-assembled it and put it back on the car following a fitting guide I found on here. Everything worked well when I checked the brake lights so I parked it up and left it.

Today when my son got in the car to take it for a test drive. He adjusted his driving position including the steering column position and off we went.

 

Within 50 meters the glow plug light started flashing. I checked the brake lights and they're still working fine.

 

Having read other bits on here it could just be it actually needs a new switch for the brake lights but could it be something else?

 

Where and how would I check for any fault codes to help find the problem?

Buy a complete new brake light switch

Should sort your issues