I have a good one that I could use some expertise on. Headlights off = tach works perfect. Headlights on = tach sticks at various RPMs. If I punch it to pass someone, it will stick somewhere on the dash and not change until I hit a bump. Never noticed it until I changed the guage face to white. I thought it might be getting hung up on the guage face itself but it doesnt do it with the lights off. WTF? Any input?