Peter,
Often times when wiring male and female pins are installed into a connector, the "wings" on the pins do not travel far enough to lock into position. Consequently when both halves of the connector are pushed together, 1 pin can push the mating pin back out of the connector. Now even though the pins may be touching each other and giving you continuity, under a demand of amperage, it causes them to separate and give you an open circuit. When trouble shooting always inspect the pins on both sides for equal depth.
Thanks Eric, It is an endless adventure that tests the depth of your resolve!
Fred