I never thought the sensors were worthwhile either..... but the other
day the garage door was about 6" from closing, I opened the entrance
door to the house, the kittens ran out.... door is about 4" off the
ground now.... under the door they went and the door stopped and
reversed. Otherwise, there would have been kitten juice running all
down the driveway.
Now, I understand this could be a happy or sad story depending upon
your personal views with respect to cats. However, my point is that you
just never know what can happen.
Another thing to consider is that most doors are supposed to reverse if
they encounter a blockage before fully closing. I look at those eyes as
a backup to that safety - in other words I don't have to worry about
ruining the door/motor if I leave a 2x4 or something laying in the path
of the door.
To answer your question, I would guess that of the 2 sensors, one is
wired with power, and the other is the "switch". Determine which is
which, and then determine if the "switch" is normally open or normally
closed, and then short or leave the leads open as required. But this is
just a WAG on my part.
I'd think it would be easier to just install em.