Crazy problem with my PRNDL display

I have a 1999 Chevy Silverado and have a very strange problem with my PRNDL display or lights. I don't get any display for the PRNDL but all other lights work fine on the console. The only way I can get the display to light up so I can see my mileage and trip gauge is to turn on the heater and wait for a little bit for it to warm up. Or sometimes I can slap the panel at my feet just below the steering wheel and it will come on. I thought it might be a stuck relay or something but don't know which one. Any help would be greatly appreciated. Thanks in advance.