Last night, the passenger-side tail-light on my step-daughter's 2004 Mitsubishi Lancer ES went out. After determining that the bulb was OK, we looked in the fuse box, and saw that one of the two 7.5 amp fuses for the tail lights was blown. A replacement fuse immediately popped.
Today, we attempted to diagnose it with a VOM, and got some puzzling results.
With the battery disconnected, both fuses pulled and the head-lamp switch in the off position:
I read 0 Ohms across the terminals of the tail-light bulb socket (with bulb removed.) This immediately made me think "the positive side is shorting to ground somewhere between this bulb socket, and the head-lamp switch on the steering column".
However, I also read 0 Ohms across the terminals of the (separate) turn signal bulbs, which are working just fine! They use a different fuse, and turn signals/hazards were not engaged at the time, so that 0 Ohm reading really confused me.
At that point my step-daughter drove off to run an errand, and when she came back the other tail-light was out. By this point that second 7.5 amp fuse was blown. After disconnecting the battery again, I checked ohmage between the positive terminals of both fuse sockets, and measured 0. I did the same thing for the negative terminals of both fuse sockets, and also measured 0. This lead me to believe that the 2 tail-light fuses are wired in parallel together, which IIRC means they effectively act together as a 15 amp fuse? ... That also makes no sense, because if they were co-redundant, I'd have expected both tail-lights to continue shining so long as at least one of those fuses was still good.
Should I be approaching this problem in some other way? (And, for bonus points, can anyone explain the oddities described above?)