One trick is if you have a three pin connector is to use the center pin for
positive and the two outside pins connected to ground. Then polarity does
not matter.
Another common thing on multipin strip connectors is to remove a male pin
and insert a dummy plug in the matching female location. If reversed, it
will not plug in.
That reminds me. A very long time ago we were manufacturing a product with
a 12 pin in line connector with a missing pin. It turns out that a square
toothpick fit perfectly as a plug for the female connector: Just push it
all the way in and cut it off flush.
We had an angry customer calling about our terrible quality: He said there
was even a piece of wood stuck in the connector and it took him a long time
to remove it. Then even worse he said, when he finally plugged it in there
was smoke coming from the PCB and it did not work. Of course he had plugged
it in backwards.
Bertho
Bertho