Because of the low impedances of the windings a small (<100mV) voltage differential between the windings can sen a large current through the loweer voltage secondary when they are wired in parallel. How to proceed, connect one end of each winding to the other, measure the voltage across the two free ends, if its ~0V then OK, if its 2 X the voltage change the ends of one winding. When the voltage is 0V. Change the meter to measure 10A current and see how much current is flowing, then turn the meter to a lower current range. Then make up your mind.
Frank