The ATP certificated pilot and his wife had been airborne for about 35 minutes and were approaching an airport for landing when she stated that they had an inflight cabin fire. The night flight originated at Las Vegas, Nevada, where they had just been married. Prior to reaching the intended airport, she stated the fire originated in the overhead light console which houses 2 rheostats and a light switch. The fire began to burn the headliner and plastic console. The burning plastic was dripping onto their bodies. The aircraft crashed out of control near the runway in the dirt and was destroyed. The cabin fire was extinguished by the local fire department. A duplicate console was tested. When the door post light was shorted, the lighting rheostat in the console reached in excess of 1425 degrees Fahrenheit at a circuit load 6 amps maximum. The circuit is protected by a 10 amp breaker. The overhead cabin plastic material was found to readily burn.