430 is right. Switch is for dimming for night time use.
You can check each function of the monitor by using a paper clip in the connector going to the baler (tractor side). One pin is ground and I do not remember which one, but trial and error will find it without any damage. Once you find the ground, use the paper clip and go to ground and each of the other pins, one at a time. Each pin should make the monitor do something.
There is a light bulb inside of the monitor. It is used for load for one of the functions (flashing yellow light). If it is burnt out, the light will not flash. (flashing light is for approaching bale size selected)