1995 Pontiac Grand Prix Battery dies

I have a short somewhere in the electricval system. Reading in my repair manual, it says to disconnect the negative cable and attatch a test light to the negative post and the negative cable. If the light comes on there is a short, if the light does not come on disconnect the alternator harness and perform this same test again, my problem is that with my test light connected it is UNLIT... if i open the door the test light will come on.... but be very dim.... and pulsate. Once i close the door the light will stay lit very dim and after a few seconds goes out..... i don't know what to look at.

Help!