Deloonie

Door switches short to ground when the door is open and are held open circuit when the door is closed to check the switch simply remove it and tape up the cable connecter so it cannot short to the bodywork. If you still show the door open then follow the wire back along its run to see if you have any damage, be critical of any place it can flex

All good diagnostic advice so far but don't be tempted to put a bigger fuse rating in as that will lead to the loom Melting . Look at places where cables flex such as door hinge areas as they weeken with age/ constant movement