FD tach not working
 

So I did a search on the tach fix for FDs but they all lead me to old websites that dont exist anymore. My tach is stuck at 9k rpms even when theres no current to the car. I read that it could be the ignition wires but i dont see how ignition wires correlate to the tach not receiving a square or pulse wave.. another thing that I've been reading is that the solder joints could be cracked in the back of the tach? The tach just took a dump on me like 1 hour ago and it was just idling and the gauge just keep climbing and climbing til it got stuck at 9kish... lol any help or any leads into probable causes would be great (as to how or from where the tach receives the signal)