Without
any instruments?
You could put the current through your tongue, and estimate stuff based on the Ow! factor and the burn marks, I guess
Kidding aside: a current sensing resistor with a big electrolytic capacitor in parallel?
Turn on the motor, connect the cap in parallel to the sense resistor for a short moment (so it charges to the voltage of the sense resistor), then disconnect, and measure the voltage potential across the capacitor, via a much bigger resistor (to limit the cap discharge rate), with a multimeter?
Essentially, a sampling capacitor across a current sense resistor, poor man's MacGyver style.
The sense resistor would have to be really low, sub-ohm range... and wiring the cap using the wrong polarity probably leads to BANG! ... so I'm not sure how feasible this is. Probably quite dangerous, too. I probably should have not posted this.