84' Subaru GL Original

[jdgmbi1]

Okay. I have an all original 84' Subaru GL. It has a 119,000 miles on it. 

 

The RPM gauge started to get bouncy, regardless if you are at a idle, driving,...it has now bottomed out and doesn't move.

My guesses are it is either the gauge itself, sensor, fuse,...and that is all I can think of.

My question (s):

 

1. Does my theories sound close?

2. If so, how do I check for it, and how do I fix it.

3....and are there parts available?

 

Thank you in advance for any help that you can provide.