You can't measure current in parallel. If you're putting you probes at two points to measure current, you're doing it wrong. Current has to be measured in series, which requires you to cut something. That's why no one measures current. You have to calculate it. Measure the resistance and the voltage drop and use Ohms Law: I=V/R. As far as the 5v and 12v lines, those are DC. You should not be measuring them as AC, you won't' get the right reading.