Sprinter 316 Dashlight?

This Q concerns a Sprinter 316 chassis (late 2003) for a Pilote camper van. The orange coloured screens that show time/mileage/temp wont go out. They glow all the time and will only reduce in intensity if I turn down the -+ dashlight control. They used to go out as normal about 30 seconds after the ignition was switched off, now they glow all the time. This resulted in a new battery going flat battery after 10 days of non use plus the alarm system on.

The only recent electrical changes to the vehicle have been a new battery (mentioned above) about 2 months back. The fault with the dash lights has happened since then.

When the new batery went flat I disconnected it to recharge it and have monitord its decaying voltage and it seems OK, holding more than 12.9 volts after 3 days. But I have not had it connected to the vehicles during monitoring. When I reconnect it the lights come back on and do not go out.

Is there some capacitor that is powereing these lights that needs to be discharged to zero the system?

Any thoughts out there?

Thanks