Put the multi-meter on volts, then start pulling fuse's... When current drops ...
No offense but ignore this he mixed shit up.
Multimeter should have a separate terminal for the red lead to measure current. It should say fused 10A or something similar.
Disconnect the positive battery cable, connect the red lead of the multimeter from that fused input to the battery cable of your car. Connect the black lead of the meter to the terminal of the battery.
Turn the multimeter to measure current. If its real fancy you want DC Amps. It will be an A with a solid line over a dashed line, not the A~.
The number you see is the current flow draining your battery. As you pull fuses one by one this will drop. I don't know what is considered normal so try another good car first to compare. Once you find a fuse that makes the number drop see what that fuse is for and see why its using so much power with the car off.