Gauge cluster lights not working
 

So I have a 88 740 GLE non turbo. with the basic gauge cluster. I found a wrecked 760 in the junkyard so i snagged the voltmeter and installed it in my gauge cluster. Cool it works fine. Now the problem is that at night the lights done work in the gauge cluster and the heater control panel. Gauges work fine but no lights at night. All the fuses are good and nothing blown. Anybody have any ideas?

perhaps the bulbs are blown, just a suggestion to check the bulbs.