Cabin interior light not working

Hi, my interior light is refusing to work. I presumed the bulb had gone and bought a new LED bulb but all it does is flicker dimly. So I pulled the light fitting out, pulled the connector and the voltage across the connector pins is just under 4 volts. The radio is working fine and when I pull the fuse, which I gather the cab light shares with the radio the radio goes off and the voltage at the light drops to near zero.

What next experts?

Thanks

Dave

Is this just by opening a door or also manually turning it on? Maybe worth checking the door switch contacts and even opening the other door to check both door switches.