Dashboard not working?

I have this old 1980 Dodge pickup that has spent the last 5 years sitting in the yard. My dad gave it to me for my birthday and I noticed that even though the speedometer works the gas gauge or the thing that tells you what gear you are in doesn't work. I can handle the gas gauge. But it could be dangerous not knowing if I'm in reverse or drive. Can you give me any tips or what I can do to fix the dashboard??? Thank you