suggest testing with a volt meter on max voltage setting between A and C or A and B or B and C
as these may be tappings from the secondary coil and depending on where you place wires you might get different voltages .
then pick which ac voltage you require
try replacing the light just before the pint where the lights turn off
eg -- if the first 3 lights work replace light no 4 as it is possible that it is failing from an overheating component internally