Door Ajar Light Stays On

[Trip]

The red light on cluster is staying on when I hook up the battery, doors shut, and brake fluid full - does the trunk open also make this light stay on?
What else could it be? 

[Garry]

Whilst your brake fluid may be full, is the float still floating as they can get a pin hole and sink,even with the fluid full and bring on the brake warning light. Take out the float to see if it has any fluid in it.