Please ignore my last message. It's not immediately obvious, but there are 2 switches activated by the brake pedal. Not sure what the purpose of the front switch is, but there is another switch immediately behind it. The switch has an activator, the height of which can be adjusted by simply pulling it up or pushing it down. Adjusting the height sorted my problem. The switch is easy to remove by rotating a quarter turn, refitting it is a bit trickier. I had to remove the front switch to improve access.