Had some really rough rain this past three days. Got into my 1994 volvo 940 (no turbo) and I notice my speedometer needle bouncing from 70 to 30 to 50 to 0 to 70 then dead at 0 again. Why is this? I had no idea how fast I was going but gauging off the rpm's. I got back into car after 8 hours again and it was working fine for about 10 mins then started back all over again then dead again and not moving.
Any help would be wonderful

Thank you

 

I saw this happen in a dodge neon, it turned out it was a battery issue.

 

The diodes inside the speedo are acting up... Common issue. New speedo or replace the diodes.