Going back a long time, we used to run some AEC trucks with DPA pumps. When the pump was about to seize up, the quill shaft would snap. The quill shaft was the deliberate weak point in the drive to the pump. A new quill shaft would get the...
I would begin by making sure that both bulbs are correctly seated - if the bulb is rotated from where it should sit, the blob of solder on the base of the bulb could short across. So, take the lenses off, put the tail lights on, and gently...