Quoted from Pin_Guy:Positive lead on anode and negative lead on cathode? Your meter should measure around 0.08V across each diode, .5V seems high but not enough to assume the diode is bad.
Please pull F115 and retest the regulator output to ground.
Typical silicon diode is 0.7V, 0.5V is actually about right.
But I agree with pulling the F115 fuse then trying one more time. Just need to rule out that something down the line isn't pulling the 12V to ground.