Trunk Problem

I have a 2001 Saturn SL1 and I have been having a problem with my trunk. The trunk closes and locks but the light ib the dashboard that tells me when the trunk is open is light. When this happens I can't turn the alarm on. If I get the light to turn off and get the alarm on, sometimes the alarm goes off and the trunk light is back on. Is there a sensor that I could change to fix it, or anything else I could try to fix it. Any help would be greatly appreciated. Thanks.