I don't have voltmètre
You need to get one, even a cheap one, it will only cost you $10.
do you think that I can try with a lamp (9V)
No it won't work because it will take too much current and be not sensitive enough.
You say pin 16
Yes pin 16 on the SN754410 - the H-bridge chip. All the pins I was talking about were this chip:-