HELP!!! wiring for after market tach

ive been reading online and its all conflicting info:
soooo,i have a 1994 thunderbird super poop and the tach is WRONG and i cant find a stockie so im just going to use a cheap autozone aftermarket. my queston is what wire do i use to get the signal for the tach? and if someone can direct me on a whole wire diagram or explanation that would be cool.
i will buy the tach tomorrow so you guys can see exctly what wires it has..

How far off is the factory unit? Bet the cheap tach is wrong also. What about just a shift light?

when i goit w.o.t the tach pings 0 and when i let offf it slowly rises to what may be the correct rpms...but when im on the highwayt just cruising it says im at 3500rpms in over drive NO WAYY id hear the engine screaming a bit if that was the case and it did not seemk to be spinng that fast. and then when im on the highway and i w.o.t it pegs max and gets stuck there for 10 minuetes or untill i wack the cluster.
i had it out to fix my boost gauge and i knoticed if i lifted the rpm needle to the middle of the gause it would feel heavy towards the high end...????..... like it didnt want to drop back down or something.and its such a pain in the @ss getting the old cluster out and apart...last time my boost wire disconnected and it took me 2 hours to find where it plugged back into sc lovin though !

I have one if that helps.

Not sure if you were committed to aftermarket.

Paul

a stock tach? if so ya ille buy it NOW...i just got an after,arket and i tried evry wire from the coil for a signal and none..~~~~ this stupid ricer ~~~~~~~~ guess i gotta fix it the hard long ~~~~~~~~ way

you have to wire it from behind the stock cluster. it also has to be a tach that can do dis signal. I had a equis dis tach and worked fine

Was the tach bouncing....drop to zero and then work, sorta randomly?

PM sent

Paul

no. its not my alternator...i got the aftermarket working but i dont know how accurate that is either since i cant drive untill i get my radiator..
but its pegs 0 at wot on side roads then when im opff the gas it slowy rises to where it should be but on the highway it stays at 3.5k rpms and when i wot it pegs max rpm and will just sit there until i hit a big bump or smack the cluster..lol the fonze effect..