I've been there.
Open up the speedometer - 99% chance water has got inside and since the Neutral light is the lowest point - that's what gets wet. Look at the circuit board, I'm betting you will see corrosion on the back side of the board
If you are lucky - you can take a brush and brush the corrosion away and it plug it back in and see if it works. If it does - coat the circuit board with clear nail polish or something to protect it.
Most likely you will need to replace the board in order to get the Neutral light to come on - They are a common part you can get from Curtis or Donna and Derrik.
But maybe you will get lucky with brushing off the circuit board,