How is map light post to work?

You did not tell us what year and model you are working on. Which is always important.

Attached is a wiring doc for the accessory lamps for a 69 Barracuda that may get you on the right track.

Notice the Pink (Hot) originates from the red 16 lighter feed. In one posistion the Brown wire on the map switch shorts to the case or ground if you like, (one in the same when the switch is mounted in the dash frame). This allows for manual operation of the lamp when the doors are closed. The other posistion just connects the yellow feed from the (door switch's) directly to the brown and on to one side of the bulb. This allows the lamp to light when either door is opened. Pink on the other side of the bulb is always hot.

Do you have the correct bulb installed?