1985 Cadillac Deville

If you are attempting to measure battery drain, you are doing it incorrectly. For one, you need an ammeter capable of measuring in milliamps. The test is performed by placing the ammeter in series with the circuit. If you disconnect the battery negative, you would place the ammeter between the cable and the battery negative post. You need to make sure there is no loads on the system larger than the fuse that protects the meter, or you open the fuse. Typically, I take the key out, and close the doors with all windows open. I use a knife switch, but you can take a jumper wire between the cable and battery post. Connect your meter set on amps, between the cable and post as well, and remove the jumper. Now all the load is routed through the meter. It is possible, if you use the meter and no jumper, that the initial spike can blow the fuse in the meter. Dial the scale down on the meter to the lowest unit of measurement(400 mA/40 mA etc), and that is your drain. A vehicle of your vintage should be fairly low, less than 15-20 mA.

Normal or not, that reading(13v) is not a valid test for anything other than voltage drop, or battery voltage in a roundabout way. The 4.1mA is a valid reading, and rather excessive. The electric battery fuse, which fuse is it, and where? My question is, did that fuse break the circuit down, or are other circuits powered from that fuse? If other circuits are powered, you answered where the problem potentially lies, but it is still general. If this is in the fuse panel under the dash, which number corresponds to it?

I am showing #14 being electronic level control(rear height adjustment). It has two branches from the fuse block, one going to the ride height compressor, and one going to the height sensor. You could perhaps break it down by installing the fuse, then disconnecting the compressor and checking the draw, or disconnecting the height sensor and checking.