Bulb-out feature with relay

i don't see how you're going to do this with simple relays, unless maybe you do something like tie a relay in series with a 6 volt bulb..... bulb blows, relay won't turn on, which would leave the relay in the NO position for the power to go thru (and light a bulb on your instrument panel).  even then, you'd have to work it so that the relay's coil pulls the same resistance as the bulb in the "on" state (bulbs have a consideribly higher resistance when lit than when off).   the way you are most likely going to have to do it is to either find or build yourself a current sensing circuit for each bulb you want an indicator on (for the regular tail lights, not brakes or turn signals, you could build one current sensing circuit that would  detect when less current is being drawn than usual when any one of the regular tail lights are out).  it should be much simpler though if you build a circuit for each and every bulb independant from every other one - that way it can be a "go /no go" scenerio.... any current draw = good bulb, zero current draw = bulb blown = open circuit.   if you still need it, later i might toss together a couple of op amps in a few examples for some simple bulb out current sensing circuits if nobody else does.