I have that light with the arrow pointing down on my 3600. It is supposed to be an air intake restriction warning light. If the filter gets plugged, or if the precleaner/screen on the air intake tube gets plugged, there is a restrictor switch that senses the additional suction pressure and triggers an alarm.
I"ve looked in the New Holland Online Parts Store, and I do not see a restrictor switch on a 5000. I don"t have the switch on my 3600 either. So my light only works I initially turn the key on and start the tractor.
If you have one, the restrictor switch is mounted on the air intake tube. That light gets its ground circuit through the restrictor switch.