Jumpy speedometer needle

My tach and odometer display have been dead for months, and I think a new (used) instrument cluster will take care of it. But lately the speedometer needle is erratic and twitchy, but only when my lights are on. Is this cluster-related too, or a short in the light switch/wiring? Thanks...

I know the tach and display are circuit board related. Over time several solder connections will become what is called "cold solder" connections- they crack (hairline is all they will be- sometimes not even visible to the naked eye). The repair is just to resolder them..did mine and all is fine now. I did have the jumpy speedo needle, but I used a cluster out of a cirrus that I fixed (wanted a different color than the blue/green-these are orange). If you do a search, I'm sure you will find something.