I have a 1992 Camaro 305TPI with a 145mph dash. Should the tach not read when I disconnect the computer advance wire by the distributor. It is the grey plug that you disconnect to time the car. Mine does not work when this happens and I am wondering if this is how it should be?? Can anyone check their car for me???

 

The tach should work regardless since it reads the pulse from the negative side of the coil. From the few f-bodies I've seen, the timing by-pass has always been a tan/black stripe wire and usually located closer to the blowrer motor. Not saying that's correct for your car but, that my exp. with it. From the sounds of it, you're unplugging the actual tach lead from the coil (there is a connector on it for some reason I've yet to understand).