Need help with Iginition switch/starter issues

So I was having issues with my starter not cranking over when I turned the key. I installed a button to the relay and was able to get the starter to crank over when I turned the key to "on" position and hit the button. This worked well for about a year and a half until it started to "click" once again. So I went yesterday and bought a new starter relay and replaced the relay and now I cannot get the car to crank with the button or the key. If I cross over the posts on the regulator with a screwdriver and have the key switch in the "on" position the car will fire up. Also I have noticed when I turn the key to the "on" position my tachometer needle pegs out at 5000 RPM's without the engine running. If I wiggle the key switch the needle on the tach will go back to zero, but it is staying at 5000 RPM's before I start the car. After I have the car running the tach is back @ about 750-800 RPM's at idle. Any suggestions on what I can do to resolve this issue would help. The engine wiring harness has been replaced with one from another car and has no other obvious issues. I believe the wiring on the relay is correct as I replaced the wires from where they were previously connected and the car was cranking over fine before the clicking started. Battery is new as well as the starter.