When I bought the bike back in November the last owner gave me a spare regulator for it and told me that he had never had problems. Reading the web one could believe that every ST2 has problems with the generator/regulator system, and that was the reason that I changed every bulb that I could for LEDs.
Today was a warm 16 celcius with the sun shining so off I went for a quick 40 mile ride. Halfway I stopped for coffee, as I tend to, and the bike had been running fine. When I set off to head back for home I negotiated a few road junctions and opened the bike up to about 120 kmh. At that time a red light on the dash was trying to get my attention, the charge light was shining at me and the voltmeter was showing 12.3 volts. By the time I got home it was down to 11.9 volts an the ST went straight onto the bike lift.
With all the fairings removed I slaved the spare regulator into the system to see if that was the problem and bingo it was. The only problem was that the spare regulator has an extra plug on it. The original has two plugs with two wires in each and this one has another plug with two wires. Time to check the original regulator and found that one of the connectors inside one of the plugs was dirty and looked like it had been getting hot. It is quite easy to remove the metal connectors from the waterproof plastic plug with an instrument screwdriver, and once removed it was cleaned up with abrasive paper, squeezed to make a tighter fit and reconnected with some silicone grease. Bingo the system works again and there is nothing wrong with the regulator!
I think that I will get myself a spare for the future.