The lights at the back of a car include a combined rear light / brake light bulb.
Usually this is replaced when one of the lamp filaments burns out.
This gives you a chance to experiment since you now have a working filament and a disconnected wire which will work as an anode if the filament is supplied with its normal voltage. It will work as a diode if the bulb is under vacuum or as a plasma display if it contains gas.
Local repair shops usually discard such bulbs but would probably save you a few if you ask.