Tail Light Wiring Help Needed

Consider the double filament bulb as 'M', center point being ground, upper 2 points as elements. The current didn't ground so it continued traveling seeking ground. The front park circuit would find a ground at the turn indicators and/or fender mounted fixtures. If you had first removed the 'M' bulbs and then went inside the car looking for a fault... No fault found. That proves the fault to be at bulbs and sockets. We immediately suggest fault at socket ground because its where both circuit come together, middle of the 'M', and because we've seen it many times before.