Hi,
We have one of those large outdoor security lights; I think it's a mercury vapor lamp, it's the kind that turns off during the day and comes on at night. Recently, it started staying on all of the time, so we bought a new photocell and replaced it. It is the twist lock kind (like this: <http://www.Lowe's.com/pd_37492-30209-ALR-LC-208277BPLOWES_0__?productId=3438320&Ntt=photocell&pl=1&currentURL=/pl__0__s?Ntt=photocell&facetInfo=>
However, it is still staying on all of the time. Should we try another new photocell or just replace the entire fixture? The fixture is around 30 years old, and it has been known to not work for a few days after a heavy rain. Maybe I should just replace the fixture?
Thanks

The new photocell should have stopped the light from coming on in daylight. There may be a short in the twist lock outlet that is bypassing the PC and keeping it on.

Try checking the outlet wiring inside the fixture.

Since you have had other problems with the unit, perhaps it is time to replace it with something new.

I think I will most likely just replace the fixture.
Thanks

Although an old post, Kyle, what did you end up doing?
With the photocell removed, there are 3 slots, 1 is neutral, 1 constant hot, 3rd goes to the light.
If you remove the photocell and the light goes out, the photocell is shorted. If you remove the photocell and it remains lit, it is within the fixture.
You can test the light with no photocell by jumping 2 of the slots. BEWARE 1 slot is Neutral, Test which is what before jumping.

Well I went to the trouble and bought a new light, it was a 70watt sodium fixture. Tested it on the ground, and it shorted out, so I exchanged it at the store, Put that one on the pole, and Ithat one shorted out . So, I returned that. I cleaned out the mercury vapor fixture, sprayed some WD40 on the rusted parts, screws, etc. And suddenly it works again! Put it on the pole and have had absolutely no problems with. It must be at least forty years old judging by the parts inside.