I dug through your profile and found that you have the V6. Hick pretty much spelled it out for you, but I wanna throw in my 2 cents. My '98 didn't come with a tach so I bought an Equus tach from O'Reiley Auto for ~$35 and mounted it on the steering column, next to the hazard switch. It's centered so that it appears to be inside the arch of the speedometer markings when viewed from my driving position. I can see my MPH and look down a few degrees and see my RPM. I hooked mine up to the wires in my stereo power and dimmer wires, and the tach signal wire to the white wire on the ignition coil. I tried to use the white wire in the gauge cluster harness, but could not get a signal.
This is the tach I bought:
It looks and works great, but it's bright. Much brighter and whiter than the factory gauges. It's lit up by white LEDs, so it doesn't dim as much as the lights in the cluster do when I roll the dimmer wheel. I think a simple 20-cent resistor in the tach's light wire would fix this, but I don't know what value of resistor to get and I'm too busy to worry about it right now.