My mercury vapor yard light (dawn-to-dusk sensor) went out a few days ago. I turned the power off and replaced the sensor. As soon as I turned the power back on, the light bulb started to come on and then went out. Today, I replaced the bulb but it did not come on tonight after dark. I tested the power at the switch and that is good. Do you suppose I should buy another sensor and bulb just to see if one of them is bad? Also, when removing the old bulb today, I could not get it out. A sales person at Lowe's suggested squirting WD40 at the base. This worked and I got the bulb out. Is it possible residue from WD40 could cause the new bulb not to work? This task requires me get up on the roof and hang over the edge so I'm trying to those trips to the roof to a minimum.

 

Hi 'Ant,
- Have you made sure the tab in the bulbholder base is sticking out a bit , rather than flattened ? -Also, many sensors have variable controls, have you tried adjusting if yours has ? I would consider a sensor problem much more likely than the bulb.
Re. the WD-40 suggestion, I would make sure to wipe it all off when power is definitely off.

Do it Right - Do it once.