My method your method, same result. Say you do your test and you get a 8 volt drop across one of the wires when someone tries to crank the engine. Bad cable or connection. Doing it my way, I am going to get 4 volts at the same point during cranking, 12v-8v drop in bad cable equals 4v.
Are they? Under normal starting conditions can we agree that you will see a voltage drop across the battery terminals when cranking? The question though is how much voltage drop is normal. That depends on many things and can change from time to time on the same system and still be normal. For example zero degree or 100 degree will produce a different voltage drop all else being the same yet would be considered normal.
With your method I agree you will see a voltage drop but what does it mean. Can you measure tenths of a volt drop and be certain that it is normal or a high resistance connection?
"So put your meter on the posts themselves on the battery. You will most likely get 12v. But, keep holding it on the posts while someone tries to start the truck. What did the voltage do then? If it dropped, the battery has a problem. If the voltage stayed high, then move the meter leads to the battery ends of the large wires. Probably 12v again, but keep holding it there while someone tries to crank the truck. If the voltage drops, you have a poor connection on one of the battery connections."
Maybe I have miss understood what you are trying to say and if so I do apologize. That to me says you are measuring across the battery post which will tell you resting battery voltage engine not running, or when at the other ends of cable really the same thing. When cranking you would be seeing voltage drop of complete system which may or may not be normal drops.
Off subject slightly, if all you see is 12v you may not get a crank condition as that battery is down to around 30% charge. 12.8 given accuracy of most voltmeters is charged voltage.
