200tdi heated rear screen fault

My 1992 200tdi has developed a promblem with the rear heated screen it is staying on constant.

I have tested the switch and even unplugged it but it still stays on i have also unplug the relay for the screen but still no luck.
If i remove the fuse for the rear sceen the light goes out on the dash but it is still getting 12v to rear screen which is draining my battery over night
Does anyone know what could be the fault

try disconnecting the wires at the screen that should stop the drain... but maybe there is a short between the heater live and another live? would explain why you have live with switch disconnected!

Try the load relay, it sounds like the relay is welded in. The dash light is fed of the control circuit that's why the light goes out when you pull the fuse, the feed for the relay probrably comes of a different fuse of a much higher rating, heated screens are a high current user and so needa switching relay, use a 30 amp relay if you have to replace it!

Found the problem it turned out that the front of the chassis had been welded and had melted the loom that runs in the chassis for the rear lights and window heater