Chrysler Repair: Battery Drain, how to find the source., resistance one, volt ohmmeter

Question
I have a 1993 Dodge Intrepid ES (3.5l 24v).  It is loaded, has climate control, etc.  If I run the car daily it is fine, but if it sits a few days the battery will go dead.  I think it may be a motor running when the ignition is off.  I hear what sounds like a very low speed motor noise from behind the passenger side dashboard when I open the door in the morning.  Once I start it, drive and turn it off the sound goes away....but when I come back to it later and open the door, there it is.  I'm afraid this is probably starting up on its own after I shut off and lock up the car, thus draining the battery if it sits too long.  Would you know what this sound is and if it should be there when the ignition is off?  If you can also give me some pointers to track it down and fix it, that would be great.
Thanks,
John

Answer
Hi John,
The sound you hear is the in-car temperature probe's aspirator fan that is located behind the name plate on the dash. It is normal to notice it running when you open the door because opening the left side door is what starts it to run. If you don't close the door it will shut off after 5 minutes. If you do close the door but don't start the car it will shut off after 2 minutes. If the car is driven and then shut off it stops immediately. It will always run if the ignition is in the "run" position.
So there is probably something else draining the battery.
Chances are that one of the interior lights is on all the time (glove box, under the hood, in the trunk). So look carefully to see whether those bulbs are truly going off when the door is closed.
The other approach is to use an ohmmeter to measure the resistance that each of the fuses is supplying current to.
If you can get a hold of a volt-ohmmeter with a digital readout you could differentiate a too low but finite resistance from moderate acceptable resistance. One of the fuses is supplying power to a circuit with a too low resistance and that is why the battery is running down. Begin with the fuses under the hood in the power distribution center box near the battery. One pin socket of each fuse is the hot side which has 12V on it from the battery, so don't touch that one with the meter in the ohmmeter position, just use the voltmeter to find the "cold" pin after removing each fuse. The 'cold' pin is the one to measure for resistance(i.e. all the lamps and devices are attached to that one). If you set the meter to read ohms (200 ohm full scale) and touch the - lead  of the meter to any shiny metal body surface and the + lead to the cold pin of the fuse socket it should read more than 50 ohm, the more the better. Make sure all the doors are closed when you are doing the measurements.
Then the question is how to find which of the many items on a given fuse that is suspect is causing such a low reading.
So first go thru the power distribution box under the hood to find a fuse whose cold side reads less that 50 ohm, and let me know which one(s) it is (its label by number and/or purpose). That fuse will supply several fuses in the fuse box under the dash, so we will do the same testing on those fuses once we identity the 'master' fuse which is carrying too much current.
Then we can go on from there to isolate what component on that secondary fuse is drawing the current and check it out.
Roland