Map light fault - HELP!

The Switch is bad! Or it does not have a good connection from case to chassis ground.

It passes the grounding signal when either door or the headlight Dimmer switch is rotated to dome posistion.

When the doors are shut and headlight dimmer switch is normal the switch in the up posistion shorts to chassis or grounds if you like, to activate the map lamp only.

The function seems widely misunderstood. If you are driving down the road the dome coming on is a big disturbance, hence the lower mounted map light for your navigator to assist you!