John,
Like Gerald pointed out it is not likely that a solid state device would fail, especially given the situation that it restarted. Solid state devices like this one, if they fail, they remain in an open state and are not intermittent. I would look to the ignition switch itself or the plug in connector that feeds the switch connection. Also check that you do not have a loose wire on the solid state solenoid given it has been 5 years.
Sometimes if it is an ignition switch contact issue you can induce the open condition by wiggling the key, while in the ignition on position, with the engine running. If so the switch is suspect.
Later, Ed