I am not the expert here but I had the exact same trouble a while ago with my guages. It turns out it was the wiring harness under the tank that connects the guage panel to the electrical system. I am not sure if the 98 utilizes the same wiring harness as the 2000 and up. My problem was easily fixed. It was one of the wires in the harness had backed out a bit and was loose hence my dancing needles. The way I figured it out was my harness was under the tank but where I could touch it. I pushed the harness with my finger one day while riding and my needle went crazy. With a small screwdriver I was able to get the metal connecter to re-seat properly and that solved my problem. It would be something simple to check.