Please help troubleshoot nat gas Goodman furnace. Power on. Fan/blower runs constantly, but no heat. No flame. 4 blinks. No manual, but I believe this to mean "open limit" by reading other posts for this model furnace. Furnace filter was very dirty and has been replaced.

Traced wires back to what I believe is limit switch. (see image #1 in image. 2 screws removed so it is it half uninstalled and titled horizontally instead of vertically.)
swtichornot.jpg picture by mypicstrix - Photobucket

From the front, linked image below seems to match mine very well. Switch model numbers match.
Service limit switch - Product Details

However, instead of wires going out the back there is a hard black plastic rod shaped like a rocket popsicle. Maybe this is a cover? Is it removable? The limit switch has two screws which I have removed, but I am unable to wedge or angle it in such a way that it is removable. I maybe have to remove a few screws from the plate housing that holds the fan before I fully uninstall the limit switch.

Does this switch model have a reset switch?

So is this just a fuse with a sensor? If I short the wires (only for test) would the furnace run with heat?

Do big box stores have these limit switches? What kind of stores would have these or sell HAVC equipment? We are using electric heaters enough to keep things livable, but it's winter here, so help is appreciated!