My 1995 mercury grand marquis has a short somewhere and I need to find out how to trouble shoot the problem it's draining the battery and I am having to disconnect the battery when I'm not using it

with the car off disconnect the negative terminal and put a 12v tester from batt to neg cable and see how bright it is make shore switch Is off and door are close that there is no corrent is taking , disconnect fuse one by one till you see the light dims,if it dims and go off either fuse that's the short there, or check brake light if it stays on

Before pulling all the fuses one by one, (there are larger ones under the hood also), disconnect the large wire to the alternator. Sometimes the diodes go bad and drain current. make sure no dome lights or trunk or hood lights stay on (remove bulbs). I working on a Lincon right now, and can't seem to find it even with a specialized tester and 30 years exprience.