I have old garden lights which have screws on the lid/cover that have rusted solid from the salt air. I have tried using WD-40 with no luck. Any other suggestions to try ?

WD won't work because it is not a penetrant. You need something to disolve the rust. While some people actually believe that Coke will do the trick (because of the phophoric acid in it) I suggest using Vinegar. Trying pouring it over the rusted screws or cover them with a cloth soaked in vinegar until the rust has disolved. Hope this helps. Let me know.

Jersey... hope something here helps:

Rusty stuff

Vinegar, Baking Soda, Fabric Softener, and salt are all excellent ways to bust through rusty parts.

BUT, they will also promote rust as well.

I would suggest scrubbing the heads of the screws with baking soda mixed with enough water to make a paste. If the screws are counter sunk, use a tooth brush around the edges. This removes the majority of the rust and will allow for the second part.

Pour vinegar on the screws, let it sit for about an hour, try your screwdriver, if they are still tight, add more vinegar wait another hour. Sooner or later it will give, or be completely eaten away.

If the body of the light fixture is metal as well, especially a dissimilar metal, say aluminum, it may very well be that these guys are permanently welded together - salt water carries a slight charge which bonds some metals together.

That leaves you with the next option, drilling the screws out. Since you do not know what size the screw is, use a drill bit that is slightly smaller than the drill head - check often until you have drilled through the head.

The lid, or cap, may be placed in such a way that when you drill out the screw heads it will slip off, if this is the case then you can try pliers on the numb of the screw left.

If not, you can drill out the rest of the screw.

There are self taping screws, that means they will make their own threads as they enter a slightly smaller hole than their diameter. you would have to get these to replace the ones drilled.

You may need to replace the screws in any case, if this is so, get brass screws, or galvanized. These are resistant to corrosion.

After you screw them in, use any kind of nail polish, painting the whole head, and down around the sides to prevent water from getting at them again.

Cheers

David

(Oh, fabric softener will remove rust, and it will also lubricate the threads - it just takes a much longer time.

Salt can be mixed with the baking soda paste, it helps to cut through rust deposits faster)