307 Cruise control issue

Hi, I have a 2litre diesel 307 build date 2006. It has CC & speed limiter function from the factory. when the switch is rotated to engage either CC or Limiter the dashes (speed indicator) on the dashboard "flash" and you cannot select a desired speed. The dash does display CC or LIM so I guess the switch itself works i.e the system knows you are wishing to use the capability. I did have a brake light bulb out which I fixed...still no luck. The 3 brake lights all function correctly (i.e illuminate when the brake pedal is depressed and are otherwise not permanently illuminated). I couldn't find a specific fuse in the owners manual so I checked them all and they are OK. I could replace the brake switch and just hope this solves the issue but I am reluctant to go down a trial and error path replacing parts that don't need to be replaced. Any feedback on what might be the root cause OR other troubleshooting tips would be appreciated. Thanks