Map light fault - HELP!

[cruiser]

Hello FABO friends, Cruiser here. New to this forum. Anyhow, could anyone help with a weird failure mode that I'm experiencing in my very stock 74 Duster? You can view the car "Bob's 1974 Gold Duster" in the member rides section. Anyhow, it's extremely stock and the under dash wiring hasn't been messed with. When I turn on the map light switch, the map light doesn't come on. The bulb is good, and all wiring looks good. When I open the door, the dome light comes on as it should, as does the map light. But then if I activate the map light switch, the map light goes off. At night, driving with the lights on, the map light will not come on when I activate it with the switch. But if I rotate the interior lights rheostat to full bright and activate the dome light, the map light comes on, and again if I activate the map light switch at that moment, the map light goes off. Something is bass awkward here. For normal night driving, turning on the map light does nothing. Any ideas here?

 

[1969383S]

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!

 

[1969383S]

Had to edit Matt as I left out the a good chassis/ground connection.

Check for continuity between a know good chassis ground and the map lamp switch case. If you have good continuity then suspect a bad switch.

 

[triumphman]

Since your ride is original and 45 years old, the not messed with under dash harness WILL be problematic. Take an afternoon and check all grounds. Not offering a solution to your particular issue but be aware. Oh, and where some type of glasses when looking up. ( To keep the rust particles from getting in your eyes, and keep your mouth closed too