Landing Gear Lights-Need Wiring Help

Hello,

I'm replacing the landing gear down indicator lights and the transition
light in a Lancair 235. The installed lights are the kind that snap into a
hole in the panel, and the bulb is not accessible without removing the
entire light fixture.

I'm replacing those with the push-to-test type of lights found on most
certified aircraft (MS25041). The advantage being that one can check a
non-illumnating light to determine wether the circuit is open, or the bulb
is bad. The bulb can also be replaced from within the cockpit.

The dilema I am having is how these lights wire up: There are three
terminals on the fixture Vs. two on the old ones.
One terminal in the center and two on the outer edges. If I wire the
center(+) and one of the outer edges(-) to the circuit the light comes on
when its supposed to. However, the light won't illuminate when the
push-to-test feature is used (light pushed in).

What does the un-used terminal get wired to? An always on supply (+)?
I'm afraid to try it for fear of shorting something out. I welcome any
advice from someone who has wired these up before.

thanks in advance,
Bill Gilbert
N235JR