Wrong wire. You probably tapped into a constant on wire.

If you tap into the wrong wire, just change it to whatever applicable.

Although I doubt it, but sometimes manufacture change the wire coloring around, or there're some previous modification applied to the car. In that case, take off the map light, trace the switched wire color, then tap into the correct one.

In this particular case, + is always available, while - is where sensor controlled. So Just change the negative, try finding the correct wire.

Hope it helps.