Please note the position of the "band" on the diode and what color lead (positive / red or negative / black) is connected banded lead of the diode. Diodes are the equivalent of check valves in the world of plumbing or hydraulics. Current should only flow in one direction thru the diode. Current flow should be present when the negative / black lead of the multimeter is connected to the banded lead of the diode and the positive / red lead is connected to the opposite lead.    (click on image to