The problem lies with the hydraulic switch in the brake pipe. They often burn out as they carry too much current. I confirmed this by sawing one in half and the contacts were knackered.
I fixed it by putting a relay in the electrical circuit. Ideally the relay should have a diode in it and a small capacitor fitted across the hydraulic switch to eliminate internal sparking.
These are the details:
http://homepages.donobi.net/sufuelpumps/Other_Subjects/Electrical/General/Brake_Light_Relay.pdfMore recently it has occurred to me that a more elegant way of dealing with the problem would be to fit LED brake light bulbs as these take much less current.
John
