Analog to digital gauges.

i went to the junkyard the other day and pulled some digital gauges from a probe. i installed them in my car which has the analog gauges, i plugged the connecters in and the gauges didnt light up or show any sign of working. is there something i have to do to get it to work, or do the digital gauges not work on probes that didnt come stock with them?
thanks for any help you can offer me.