Look at that connector with the catch up. Connect the voltmeter leads to the upper right and lower left wire connectors and switch the ign to on. You should see a series of needle movements. Long time movements are the tens place in a two digit number, and short time movements are the ones place. For example two long pulses and three short pulses would be 23. A constant string of same length pulses means no error codes. If it swings over to about 12v and stays there, the ecu is bad.

You need to set the gauge on a range (like 0-20v DC) that puts your expected voltage near the middle of the scale. Your voltmeter will almost always be set on 20v DC for car work.