Let's take the easy route
Let's start with the simple first. Remove your drivers side kick panel so you have access to the dash lights. Remove each one and check them to see if they are burned out or if the black holder is firmly twisted in place without any corrosion on either contact point. If after doing this the problem still exists, let me know. From what you have said, it sounds like a bulb or bulb holder connection that is giving you problems.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan