s3 brake lights staying on when engine running? any ideas?

Pedal switch, probably.  Disconnect and see if they go out.

only staying on when engine running! they work as normal when engine not running?

Hahaha!  That's a beaut.  So with ignition off, they're off, ignition on, they work correctly, and engine running, they're on?

 

So, still disconnect the switch to work out if the feed is from elsewhere.  If they're still on, trace back from the bulb holder.

sorted it, just a minor adjustment to the switch, as the engine starts the servo moves the pedal a hair and put on the lights!!