now the way i see it, the point of getting an aftermarket tach is to get a more accurate tach (at least thats why im getting one) but what causes the innacuracy in the stock tach? is it the signal form the coil (blue wire)? or is is the innaccuracy in the stepper motor of the stock tach?
It is the blue wire off of the dizzy that you want to hook into... .hook that to the pulse wire on the tach. and then there is usually a power a ground and a wire to illuminate it by running it to your dash lights. .
I was running an autometer pro comp 5 inch in my old rex and the difference between that and the stock tach was about 200 RPM's. .
Many people use the aftermarket tachs because they have the ability to accellerate the needle faster than the dampened stock ones. In some cars, probably not ours, the manufacturer puts a circuit on the tach to smooth it out, to slow the speed at which it reacts. This is so when it's at idle you don't see as much fluctuation and change. People were thinking that there was something wrong with their cars because the idles weren't rock stable so the factories dumbed them down. Some newer cars even have the computer controlling the tach, so it literally is being told by the computer what rpm to read no matter what the engine is actually doing.