Interior light comes on when driving

It’s probably the door latch on that door

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its a switch with a rubber cover on it you can push it in and out, may just need a clean with some wd40 as they rarely go unless water is getting in the back of them.

is there a rheostat for the dash light, usually a round thumb wheel ,driver hand book will give details,other than that the bulb may be starting to burn out

The serpentine belt diagram for the Mercedes Vaneo 1.7 CDI may be in the belt routing booklet at this link

I think this may be the "closer" motor continuously trying to gain a positive latch--and unable to do so. This could be from a damaged latch switch.

The sliding door has three motors, a slide motor, a release (or unlatch) motor, and a closer (or latching) motor. The open door light and interior lights coming on seem to indicate that the "closed and latched" switch is sometimes open-- allowing the closer motor to continue to operate.

Another possibility is that the dent has changed the geometry of the door mechanism especially the draw of the pull cable. The slide motor has a sensor that pulses when it runs. The door management controller counts the number of pulses of the slide motor sensor to determine when the door is fully closed and then stops the slide motor. At that point, the closer motor operates to latch the door. If the cable geometry has changed, the door controller may be shutting off the slide motor prematurely and the closer motor cannot complete the latch.

BMW and Mercedes had the same problem. They changed the type of grease used to assemble the door latch mechanism.

WD40 Squirted into the lock area often does the trick.

Roll down the window and aim nozzle/straw at interior latch mechanism.

Put WD40 straw into key hole and squirt .

renew the rear springs

I had the same problem and found that my sliding side door "closed" switch, which is small and round and in the door frame, was not being pushed open all the way when the door was closed! As soon as I put a credit card in the spot where the switch hits the door all the locks and lights worked again. So I just taped a washer to the door where the pin switch hits it for now. The computer thinks the door is still open and will not alow them to lock and the lights won't operate right either.