I frequently troubleshoot automotive wiring by looking at and tracing the current flow. It's a MUCH better way of troubleshooting some problems, such as mysteriously draining batteries, than by trying to look at voltages. What I do is to find a junction that I can break AND that I can also that I can connect amp meter probes to something on each side of. I connect the amp meter probes BEFORE I break the connection and then break the circuit. That way I never lose power to the automobile's circuits. After I'm done checking, I reconnect the junction, then remove the amp meter and I don't have to reset the alarm, the clock, the radio code, stations, etc etc.
One place that I can usually break a junction is at the battery. I can't reliably connect to most battery posts so that's out but frequently the wires connecting to the various major devices are bolted to the battery clamp so I can connect one side of my amp meter to the battery clamp and the other to the wire. After the meter is set and connected, just unbolt that one wire and start reading.
If there's no place to connect the amp meter to on the battery side I have resorted to having a helper push a probe against the top of the battery post and holding it there while I unbolt the clamp and slide it off of the post (thus breaking the circuit). I then have the helper hold the clamp above the battery post and with the insulated probe sticking through the clamp. As long as they can hold everything in place, you're go to go! Obviously this is only good for checks that you can make quickly. But if you need more time they can just slide the clamp back on the battery post and take a break while you figure out what to do next.
PS: To avoid the possibility of shorting the battery, it's better to connect the amp meter in the return (aka ground) circuit instead of the "hot" side whenever possible. That way if you accidentally short something to ground there's little if any voltage difference and no current flow.