Nice and clean, good used unit, in good working condition!  This bulb failure relay is what measures the resistance over the exterior lighting, and controls that bulb on the dash that lets you know if a bulb is out.  It also acts as a passthrough for the tail and corner light voltage, so if defective not only will your tail light out bulb not work in the gauge cluster, but the exterior light may not work either.  If you are having poor function of the lights, this may be your problem.  It is also a good idea to check and clean your ground points for the lights, as this will cause a similar issue to this relay being faulty and you can't tell what the issue is unless you do this first.