My tach was hung at around 6 grand and had no idea what was up. After tearing down and checking every connection I was stumped. Then I unplugged the shift light and it went back to normal. Checked the wiring to it, and the bulb. The bulb looks just fine, wiring looks fine. Turned out the bulb itself was bad, even though it looked fine. thought it may be a handy tip for you guys before you go tearing down like I did.