Lighting, Light Fixtures, Ceiling and Exhaust Fans - Replacing Exterior Flood Light

I need some serious help replacing an exterior flood light. The existing flood light is a two bulb, non-motion activated, and I want to replace it with a motion activated light. I took the old light apart, and each bulb was wired individually, with a white and black wire. The new motion activated one is only two wires, again white and black. I first tried wiring up one pair of wires, then the other, and then all the wires together (all the whites together and all the blacks together) In no combination could I get the new flood light to come on. I started investigating with a volt meter, and i do have 110 between the black and white, and between the black and the box, no matter if the switch is in the on or off position.

What is it I don't get? Obviously the black is the hot, and the box is grounded, but why do I have voltage all the time? Further, with voltage all the time, why can't I get my new light to work? I'm not very experienced with this sort of thing, but it shouldn't be this hard.

Was it dark when you did this work? Motion sensors also are associated with light sensors, so it has to be dark, or you have to move the selector to "test" in order for it to come on. How many wires do you have in the light box? It appears you have a hot wire and a switch loop, which we will have to determine. Is there any way you can post a picture of the junction box where you took down the light on a site such as photobucket.com and copy/paste the IMG code to your reply post.

The light was in the "Test" mode, although I will admit so far i haven't been doing this in the most favorable lighting conditions so far. The light box has four wires, two white and two black, that were originally wired to the two separate bulbs of the non-motion activated light. The wires come down from the center of the light box, from a piece of threaded tubing a little less than a half inch in diameter, just enough room for the four wires to come through.

Does any of this help?

In a switch loop situation, the white wire is sometimes used to carry current to the switch and return on the black wire. So, were the blacks tied to each other as well as the whites originally? Are there any downline lighting units on this circuit?

The wires were not tied together. One white and black wire went to one bulb on the original flood light, and the other white and black wire went to the other bulb. There is no other lights on this switch.

The way the old fixture was wired sounds unusual. Normally all the blacks would have been together and all the whites together.

As it was you would have needed both blacks to be hot in order for the fixture to work properly.