What will cause the rpm. And oddmetter and speed not to work and my dash borad trun on and off

...yes, easy one...the chassis ground is not making enough of a connection to supply grounding to the dash....you must disassemble the main ground connection (battery to frame) the frame needs to be wirebrushed clean with a coarse wirebrush and the lug too....little known fact, everytime you start the car there are bits of the lug and bits of the frame exchange particles in a firey connection....this corrodes the connection...as you will see when you disassemble this connection to clean it~....also if the battery is older than five will need replacement....these new tin/antimony alloy batteries (no lead anymore) will stop accepting a charge ten percent per year....so get a NEW one~

something similar happened to me a few years ago. My alternator was about to croak, and those symptoms were persistent until if finally went on to the other side. I hope this helps.