If you are looking for a circuit drain, you will have to use the current function on your meter. With everything powered off, disconnect the negative battery lead in the engine compartment. Put the positive probe of your meter on the battery negative terminal and the negative meter probe on the negative cable end. Switch your meter to read Amps/Milliamps and read the current. Start pulling fuses one at a time to find the culprit.
After you find the offending circuit, you will have to isolate ( if possible) each section to find the drain ,usually a short to ground. If you have a schematic or know the circuit, apply power to the circuit and start taking voltage measurements at each point along the way. If it measures 12.69 at one end , and anything a volt or so less at the next junction, you have found the problem. If you do not know the circuit, you will have to trace it with the continuity section of your meter. Remove power from the system, put one probe on one end of the circuit, and use the other probe to confirm the other end.
You should also check, clean and re-seal all grounds that would even remotely be involved. If those pesky little electrons can not find their normal way back home because a ground is bad, they will find all sorts of creative ways to complete a circuit or make a new one. Sometimes it is not the one you are working on.
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Gary Gilliam Sumerduck VA, '94 940 na Regina 150k, '86 240 180k