Let me chime in by saying you should do exactly what RPM55 told you and CSNOW spelled out for you. You don't want to disconnect the battery negative cable before the two probes are in place. With the meter probes attached to the battery terminal and to the car's ground and the meter set to DC current your car's elctrical system will not be powered down momentarily when you disconnect the negative cable. That is what you want to do. If you don't understand what they said print out and have someone handy with basic electricity help guide you.
A multimeter acts like a closed circuit when measuring current and as an open circuit when selected to measure voltage.
1982 300D Turbo