Tom Blankinship is right - different cars are wired differently and we shouldn't assume which one is for the charging circuit and which is for low oil pressure.
And Robert's right, too - the Vintage Speedster manual does say the left is oil pressure and the right is charge.
BUT - my brand new 2013 VS came wired just the opposite. How did I find out? There's a simple test.
With the engine not running and the ignition on, both lights should be on. Check your alternator and you'll find two wires connected to it - a heavy gauge wire connected to the 'B+' terminal and a thinner gauge wire connected to another terminal.
Unhook the THINNER GAUGE wire from the alternator and one of the lights should go out. THAT's the charging light. The other is oil pressure.