Dave wrote:
I have to outdoor light fixtures (four sockets) that have been empty
for several years.
....

I'm afraid that the threads in the sockets will be a bit corroded.

Think?

Can I spray WD-40 into the sockets, let it sit for a while and then
install the bulbs?

You can, but it would be far better unless they're in better shape than
one would expect to do a good job of cleaning them up first. I tend to
use the automotive-style dielectric grease (like you find in tail light
fixtures, etc.) in outdoor sockets to minimize the inevitable corrosion.

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