Warning Lamp Volvo Kamd 44p

[Bullish]

There are four warning lamps on the dash. The furthest one to the right for my starboard engine came on during my last trip to the canyon. The book said, " lamp not used". I inferred this to mean that it is an extra warning lamp not hooked up to anything. So we continued our trip and returned home without any problems although the warning lamp remained on the entire trip.

Anyone else had this happen? If so, is my assumption correct....it means nothing?