When carrying out a parasitic battery drain test, it is important not to disturb the battery power supply, by disconnecting the terminals.
If you do, you risk placing the vehicle into a different condition to it’s normal sleep condition or resetting any faults present in an electronic module. There is also a chance of damaging electronic modules when disconnecting or reconnecting the battery.
There are many methods of parasitic drain testing, some being quite expensive. But if you have a digital multimeter (DMM), with amps capability, then you have enough equipment. However, you may need additional test leads or connectors, to achieve this.
Remember: your multimeter is only as good as the connection you make, so investing in good quality test leads with interchangeable ends is a great move.
In order to carry out the test, you will need to set the vehicle up prior to testing. Some modern vehicles can take up to an hour to completely shut down. In some instances, that can be longer depending on the equipment level.
By ‘setting up the vehicle’ I mean making sure the vehicle has been run, switched off and key removed. Then making the vehicle accessible for testing, without disturbing it. This means open the doors necessary to access fuse boxes and equipment, latching the door locks or opening pin switches, to allow the vehicle to believe the doors are closed. It is preferable to lock the vehicle, so that it’s in the condition it would normally be in, but that might prove difficult if it has an alarm with interior movement sensors. In that case, I recommend not locking it to carry out the test, in the first inspection. You might have to wait a little longer for shut down, but I have not yet found a fault that was only present with the alarm active. Eliminate everything else first.
Once all the doors are set, including glove boxes which hide fuse boxes, go ahead with the installation of equipment.
Check out this short video showing the setting up of a parasitic drain test on a vehicle, using a multimeter connected in series to the battery negative terminal.
Parasitic Drain Test: https://youtu.be/CbAtGMAG2Hw