Yes, the instrument panel circuit board is completely separate from the ECU. No, electronically speaking, there is no reason why dimming the lights would cause it.
Most speedometers these days utilize a stepper motor to drive the speedo needle. A stepper motor is a type of motor that is minutely controllable, and, unlike other types of motors, doesn't "creep" after power is removed and doesn't require a motor brake to stop the output instantaneously. A servo is similar, but not exactly identical. Logically, this motor is integral to the instrument panel.
Sunday, October 9th, 2011 AT 4:14 AM