ugh.....

so ya, i buy the car. tach works awesome....no problems works perfect,

a couple days ago i put a deck in and cut some wires here and there...anways....i ended up cutting a wire from the tach....witch i though was its ground...being a black wire....anyways i was wrong and it was actually a keyswitch, so i wire it to the back of my fusepanel and it works fine....for a couple days

so on my way to work i notice it wasnt working right, like it has pwer and all( the light in the tach itself is on) and it works but is not reading close to the right reading....like one second its half my rpm's the next its at like 10 grand,... so when i rev the engine it goes ultra high but while im at like 3500 its reading like 1-2 grand...i checked most of the wires....i didnt ever touch the power or the ground so theres no problem there....the key@!#$ch still works because my deck still is working fine....i didnt touch the wires that went from the tach to the engine plug....but i checked them and they seem fine, ...and are still in the plug tight....

the model of the tach is the ractive G1000 (it came with the car...and worked fine....)

this has me really stumped....any help out there?