How do you measure the input from the ECU to the ignitor (ICM) (YEL/GRN wire)????

This input tells the ignitor when to ground the -ve side of the primary coil.

My multimeter registers a non zero small voltage when cranking, but since the response is very low on my meter, I dont think im picking up the correct voltage.

Should I be using a PC oscilloscope? If so so what voltage should I see