Are you getting a lamp-out warning when you step on the brakes? You should be - it's the yellow indicator on the dash with the lightbulb symbol.

The bulb is a dealer-only item. It's halogen.

I ran circles trying to get the lamp warning light to go out on my car without success - the 3rd stop lamp was the culprit, as the PO had replaced the halogen bulb with a standard bulb. Fewer watts to drive the standard bulb = light out circuit thinks the bulb is out.

The wire for the lamp runs under the rear package shelf towards the passenger side of the car and from there into the trunk.

It's most likely the bulb.