My tach jumps too high and all weird when i turn my lights on. What's up with that? Only when the lights are turned on.

 

Check all your ground straps. Sounds like a ground problem.

 

I would check the 12v power wire that goes to the tach. On the speedo this wire is red with a black stripe is the constant positive. I would disconnect it and check the voltage of it... see if it jumps when you turn your lights on.