Occasionally upon startup, the instrument panel lights on my '96 Passat TDI will not come on. These lights and gauge needles will also temporarily drop to 0 while driving with no change to performance. Yesterday, a tap to the dashboard caused the lights to come back on at start-up; however, shortly before driving off the CEL came on and stayed on. The CEL continues to come on about 15 seconds after turning on the engine and remains on for the duration of my trips. Any pointers would be greatly appreciated!